diff --git a/crates/persistence/src/backends/sqlite/search/query_builder.rs b/crates/persistence/src/backends/sqlite/search/query_builder.rs
index c64b89036..a8e54e9f8 100644
--- a/crates/persistence/src/backends/sqlite/search/query_builder.rs
+++ b/crates/persistence/src/backends/sqlite/search/query_builder.rs
@@ -382,8 +382,18 @@ impl QueryBuilder {
         param: &SearchParameter,
         param_offset: usize,
     ) -> Option<SqlFragment> {
-        // Handle special parameters
-        if param.name.starts_with('_') {
+        // Handle special parameters. `_tag`/`_profile`/`_security`/`_source`
+        // are NOT special on the query side: the extractor indexes them from
+        // meta like any typed parameter (rows in search_index under their own
+        // param_name), so they take the regular token/uri path below. Routing
+        // them into the special handler silently dropped the condition and
+        // returned the unfiltered result set (#474).
+        if param.name.starts_with('_')
+            && !matches!(
+                param.name.as_str(),
+                "_tag" | "_profile" | "_security" | "_source"
+            )
+        {
             return self.build_special_parameter_condition(param, param_offset);
         }
 
diff --git a/crates/persistence/tests/search/meta_params_tests.rs b/crates/persistence/tests/search/meta_params_tests.rs
new file mode 100644
index 000000000..0cf06fb14
--- /dev/null
+++ b/crates/persistence/tests/search/meta_params_tests.rs
@@ -0,0 +1,158 @@
+//! Tests for the meta search parameters `_tag`, `_profile`, `_security`,
+//! and `_source` (#474).
+//!
+//! These are ordinary typed parameters indexed from `Resource.meta.*` by the
+//! spec `SearchParameter` set; the query builder must apply them rather than
+//! treating them as unimplemented specials and silently returning the
+//! unfiltered result set.
+
+use serde_json::json;
+
+use helios_persistence::core::{ResourceStorage, SearchProvider};
+use helios_persistence::tenant::{TenantContext, TenantId, TenantPermissions};
+use helios_persistence::types::{SearchParamType, SearchParameter, SearchQuery, SearchValue};
+
+use helios_fhir::FhirVersion;
+
+#[cfg(feature = "sqlite")]
+use helios_persistence::backends::sqlite::SqliteBackend;
+
+#[cfg(feature = "sqlite")]
+fn create_sqlite_backend() -> SqliteBackend {
+    super::make_sqlite_backend()
+}
+
+fn create_tenant() -> TenantContext {
+    TenantContext::new(
+        TenantId::new("test-tenant"),
+        TenantPermissions::full_access(),
+    )
+}
+
+#[cfg(feature = "sqlite")]
+async fn seed_meta_patients(backend: &SqliteBackend, tenant: &TenantContext) {
+    let tagged = json!({
+        "resourceType": "Patient",
+        "meta": {
+            "tag": [{"system": "http://example.org/tags", "code": "test-data"}],
+            "profile": ["http://example.org/StructureDefinition/custom-patient"],
+            "security": [{
+                "system": "http://terminology.hl7.org/CodeSystem/v3-ActCode",
+                "code": "HTEST"
+            }]
+        },
+        "gender": "female"
+    });
+    let untagged = json!({"resourceType": "Patient", "gender": "male"});
+    backend
+        .create(tenant, "Patient", tagged, FhirVersion::default())
+        .await
+        .unwrap();
+    backend
+        .create(tenant, "Patient", untagged, FhirVersion::default())
+        .await
+        .unwrap();
+}
+
+fn token_param(name: &str, system: Option<&str>, code: &str) -> SearchParameter {
+    SearchParameter {
+        name: name.to_string(),
+        param_type: SearchParamType::Token,
+        modifier: None,
+        values: vec![SearchValue::token(system, code)],
+        chain: vec![],
+        components: vec![],
+    }
+}
+
+#[cfg(feature = "sqlite")]
+#[tokio::test]
+async fn test_tag_filters_to_tagged_resources() {
+    let backend = create_sqlite_backend();
+    let tenant = create_tenant();
+    seed_meta_patients(&backend, &tenant).await;
+
+    let query = SearchQuery::new("Patient").with_parameter(token_param(
+        "_tag",
+        Some("http://example.org/tags"),
+        "test-data",
+    ));
+    let result = backend
+        .search(&tenant, &query.with_count(100))
+        .await
+        .unwrap();
+
+    assert_eq!(
+        result.resources.len(),
+        1,
+        "_tag must filter, not fall through to the unfiltered set"
+    );
+    assert_eq!(result.resources.items[0].content()["gender"], "female");
+}
+
+#[cfg(feature = "sqlite")]
+#[tokio::test]
+async fn test_tag_with_no_match_returns_empty() {
+    let backend = create_sqlite_backend();
+    let tenant = create_tenant();
+    seed_meta_patients(&backend, &tenant).await;
+
+    let query = SearchQuery::new("Patient").with_parameter(token_param(
+        "_tag",
+        Some("http://example.org/tags"),
+        "no-such-tag",
+    ));
+    let result = backend
+        .search(&tenant, &query.with_count(100))
+        .await
+        .unwrap();
+
+    assert_eq!(result.resources.len(), 0);
+}
+
+#[cfg(feature = "sqlite")]
+#[tokio::test]
+async fn test_security_filters_by_security_label() {
+    let backend = create_sqlite_backend();
+    let tenant = create_tenant();
+    seed_meta_patients(&backend, &tenant).await;
+
+    let query = SearchQuery::new("Patient").with_parameter(token_param(
+        "_security",
+        Some("http://terminology.hl7.org/CodeSystem/v3-ActCode"),
+        "HTEST",
+    ));
+    let result = backend
+        .search(&tenant, &query.with_count(100))
+        .await
+        .unwrap();
+
+    assert_eq!(result.resources.len(), 1);
+    assert_eq!(result.resources.items[0].content()["gender"], "female");
+}
+
+#[cfg(feature = "sqlite")]
+#[tokio::test]
+async fn test_profile_filters_by_canonical() {
+    let backend = create_sqlite_backend();
+    let tenant = create_tenant();
+    seed_meta_patients(&backend, &tenant).await;
+
+    let query = SearchQuery::new("Patient").with_parameter(SearchParameter {
+        name: "_profile".to_string(),
+        param_type: SearchParamType::Uri,
+        modifier: None,
+        values: vec![SearchValue::string(
+            "http://example.org/StructureDefinition/custom-patient",
+        )],
+        chain: vec![],
+        components: vec![],
+    });
+    let result = backend
+        .search(&tenant, &query.with_count(100))
+        .await
+        .unwrap();
+
+    assert_eq!(result.resources.len(), 1);
+    assert_eq!(result.resources.items[0].content()["gender"], "female");
+}
diff --git a/crates/persistence/tests/search/mod.rs b/crates/persistence/tests/search/mod.rs
index 1dbf97dc7..0fc0c3f74 100644
--- a/crates/persistence/tests/search/mod.rs
+++ b/crates/persistence/tests/search/mod.rs
@@ -41,6 +41,7 @@ pub fn make_sqlite_backend() -> SqliteBackend {
 pub mod chained_tests;
 pub mod date_tests;
 pub mod include_tests;
+pub mod meta_params_tests;
 pub mod modifier_tests;
 pub mod number_tests;
 pub mod pagination_tests;
diff --git a/crates/rest/tests/search_integration.rs b/crates/rest/tests/search_integration.rs
index c0094311a..329107839 100644
--- a/crates/rest/tests/search_integration.rs
+++ b/crates/rest/tests/search_integration.rs
@@ -2577,3 +2577,73 @@ mod summary_count {
         assert!(body["total"].is_null(), "explicit _total=none wins: {body}");
     }
 }
+
+// ============================================================================
+// Meta Parameter Tests (_tag / _profile / _security, #474)
+// ============================================================================
+
+mod meta_params {
+    use super::*;
+    use helios_persistence::tenant::{TenantContext, TenantId, TenantPermissions};
+
+    async fn seed_tagged_patient(backend: &SqliteBackend) {
+        let tenant = TenantContext::new(
+            TenantId::new("test-tenant"),
+            TenantPermissions::full_access(),
+        );
+        let tagged = json!({
+            "resourceType": "Patient",
+            "meta": {
+                "tag": [{"system": "http://example.org/tags", "code": "test-data"}],
+                "profile": ["http://example.org/StructureDefinition/custom-patient"]
+            },
+            "name": [{"family": "Tagged"}]
+        });
+        backend
+            .create(&tenant, "Patient", tagged, FhirVersion::R4)
+            .await
+            .unwrap();
+    }
+
+    #[tokio::test]
+    async fn test_tag_filters_over_http() {
+        let (server, backend) = create_test_server().await;
+        seed_search_test_data(&backend).await;
+        seed_tagged_patient(&backend).await;
+
+        let response = server
+            .get("/Patient?_tag=http%3A%2F%2Fexample.org%2Ftags%7Ctest-data")
+            .add_header(X_TENANT_ID, HeaderValue::from_static("test-tenant"))
+            .await;
+
+        response.assert_status_ok();
+        let body: Value = response.json();
+        let entries = get_bundle_entries(&body);
+        assert_eq!(
+            entries.len(),
+            1,
+            "_tag must filter instead of returning every patient"
+        );
+        assert_eq!(entries[0]["resource"]["name"][0]["family"], "Tagged");
+    }
+
+    #[tokio::test]
+    async fn test_profile_filters_over_http() {
+        let (server, backend) = create_test_server().await;
+        seed_search_test_data(&backend).await;
+        seed_tagged_patient(&backend).await;
+
+        let response = server
+            .get(
+                "/Patient?_profile=http%3A%2F%2Fexample.org%2FStructureDefinition%2Fcustom-patient",
+            )
+            .add_header(X_TENANT_ID, HeaderValue::from_static("test-tenant"))
+            .await;
+
+        response.assert_status_ok();
+        let body: Value = response.json();
+        let entries = get_bundle_entries(&body);
+        assert_eq!(entries.len(), 1);
+        assert_eq!(entries[0]["resource"]["name"][0]["family"], "Tagged");
+    }
+}