diff --git a/pkg/services/ngalert/notifier/alertmanager.go b/pkg/services/ngalert/notifier/alertmanager.go
index 2a5c1374186..f6aefceae38 100644
--- a/pkg/services/ngalert/notifier/alertmanager.go
+++ b/pkg/services/ngalert/notifier/alertmanager.go
@@ -49,8 +49,6 @@ const (
 	silencesFilename        = "silences"
 
 	workingDir = "alerting"
-	// How long should we keep silences and notification entries on-disk after they've served their purpose.
-	retentionNotificationsAndSilences = 5 * 24 * time.Hour
 	// maintenanceNotificationAndSilences how often should we flush and gargabe collect notifications and silences
 	maintenanceNotificationAndSilences = 15 * time.Minute
 	// defaultResolveTimeout is the default timeout used for resolving an alert
@@ -60,6 +58,10 @@ const (
 	memoryAlertsGCInterval = 30 * time.Minute
 )
 
+// How long should we keep silences and notification entries on-disk after they've served their purpose.
+var retentionNotificationsAndSilences = 5 * 24 * time.Hour
+var silenceMaintenanceInterval = 15 * time.Minute
+
 func init() {
 	silence.ValidateMatcher = func(m *pb.Matcher) error {
 		switch m.Type {
@@ -185,7 +187,14 @@ func newAlertmanager(ctx context.Context, orgID int64, cfg *setting.Cfg, store s
 
 	am.wg.Add(1)
 	go func() {
-		am.silences.Maintenance(15*time.Minute, silencesFilePath, am.stopc, func() (int64, error) {
+		am.silences.Maintenance(silenceMaintenanceInterval, silencesFilePath, am.stopc, func() (int64, error) {
+			// Delete silences older than the retention period.
+			if _, err := am.silences.GC(); err != nil {
+				am.logger.Error("Silence Garbage Collection Failed at %v: %v", time.Now(), err)
+				// Don't return here - we need to snapshot our state first.
+			}
+
+			// Snapshot our silences to the Grafana KV store
 			return am.fileStore.Persist(ctx, silencesFilename, am.silences)
 		})
 		am.wg.Done()
diff --git a/pkg/services/ngalert/notifier/alertmanager_test.go b/pkg/services/ngalert/notifier/alertmanager_test.go
index 15804426c3f..94ec8a365fb 100644
--- a/pkg/services/ngalert/notifier/alertmanager_test.go
+++ b/pkg/services/ngalert/notifier/alertmanager_test.go
@@ -340,3 +340,75 @@ func TestPutAlert(t *testing.T) {
 		})
 	}
 }
+
+// Tests cleanup of expired Silences. We rely on prometheus/alertmanager for
+// our alert silencing functionality, so we rely on its tests. However, we
+// implement a custom maintenance function for silences, because we snapshot
+// our data differently, so we test that functionality.
+func TestSilenceCleanup(t *testing.T) {
+	require := require.New(t)
+
+	oldRetention := retentionNotificationsAndSilences
+	retentionNotificationsAndSilences = 30 * time.Millisecond
+	oldMaintenance := silenceMaintenanceInterval
+	silenceMaintenanceInterval = 15 * time.Millisecond
+	t.Cleanup(
+		func() {
+			retentionNotificationsAndSilences = oldRetention
+			silenceMaintenanceInterval = oldMaintenance
+		})
+
+	am := setupAMTest(t)
+	now := time.Now()
+	dt := func(t time.Time) strfmt.DateTime { return strfmt.DateTime(t) }
+
+	makeSilence := func(comment string, createdBy string,
+		startsAt, endsAt strfmt.DateTime, matchers models.Matchers) *apimodels.PostableSilence {
+		return &apimodels.PostableSilence{
+			ID: "",
+			Silence: models.Silence{
+				Comment:   &comment,
+				CreatedBy: &createdBy,
+				StartsAt:  &startsAt,
+				EndsAt:    &endsAt,
+				Matchers:  matchers,
+			},
+		}
+	}
+
+	tru := true
+	testString := "testName"
+	matchers := models.Matchers{&models.Matcher{Name: &testString, IsEqual: &tru, IsRegex: &tru, Value: &testString}}
+	// Create silences - one in the future, one currently active, one expired but
+	// retained, one expired and not retained.
+	silences := []*apimodels.PostableSilence{
+		// Active in future
+		makeSilence("", "tests", dt(now.Add(5*time.Hour)), dt(now.Add(6*time.Hour)), matchers),
+		// Active now
+		makeSilence("", "tests", dt(now.Add(-5*time.Hour)), dt(now.Add(6*time.Hour)), matchers),
+		// Expiring soon
+		makeSilence("", "tests", dt(now.Add(-5*time.Hour)), dt(now.Add(2*time.Second)), matchers),
+		// Expiring *very* soon
+		makeSilence("", "tests", dt(now.Add(-5*time.Hour)), dt(now.Add(20*time.Millisecond)), matchers),
+	}
+
+	for _, s := range silences {
+		_, err := am.CreateSilence(s)
+		require.NoError(err)
+	}
+
+	// Let enough time pass for the maintenance window to run.
+	require.Eventually(func() bool {
+		// So, what silences do we have now?
+		found, err := am.ListSilences(nil)
+		require.NoError(err)
+		return len(found) == 3
+	}, 1500*time.Millisecond, 150*time.Millisecond)
+
+	// Wait again for another silence to expire.
+	require.Eventually(func() bool {
+		found, err := am.ListSilences(nil)
+		require.NoError(err)
+		return len(found) == 2
+	}, 2*time.Second, 150*time.Millisecond)
+}