diff --git a/example_config.yaml b/example_config.yaml
index 90b7fc8..df80fc9 100644
--- a/example_config.yaml
+++ b/example_config.yaml
@@ -78,6 +78,10 @@ chihaya:
     # higher degree of parallelism.
     shard_count: 1024
 
+    # The interval at which metrics about the number of infohashes and peers
+    # are collected and posted to Prometheus.
+    prometheus_reporting_interval: 1s
+
   # This block defines configuration used for middleware executed before a
   # response has been returned to a BitTorrent client.
   prehooks:
diff --git a/storage/memory/peer_store.go b/storage/memory/peer_store.go
index 05ef9c7..00f9e18 100644
--- a/storage/memory/peer_store.go
+++ b/storage/memory/peer_store.go
@@ -19,6 +19,7 @@ import (
 func init() {
 	prometheus.MustRegister(promGCDurationMilliseconds)
 	prometheus.MustRegister(promInfohashesCount)
+	prometheus.MustRegister(promSeedersCount, promLeechersCount)
 }
 
 var promGCDurationMilliseconds = prometheus.NewHistogram(prometheus.HistogramOpts{
@@ -32,25 +33,31 @@ var promInfohashesCount = prometheus.NewGauge(prometheus.GaugeOpts{
 	Help: "The number of infohashes tracked",
 })
 
+var promSeedersCount = prometheus.NewGauge(prometheus.GaugeOpts{
+	Name: "chihaya_storage_seeders_count",
+	Help: "The number of seeders tracked",
+})
+
+var promLeechersCount = prometheus.NewGauge(prometheus.GaugeOpts{
+	Name: "chihaya_storage_leechers_count",
+	Help: "The number of leechers tracked",
+})
+
 // recordGCDuration records the duration of a GC sweep.
 func recordGCDuration(duration time.Duration) {
 	promGCDurationMilliseconds.Observe(float64(duration.Nanoseconds()) / float64(time.Millisecond))
 }
 
-// recordInfohashesDelta records a change in the number of Infohashes tracked.
-func recordInfohashesDelta(delta float64) {
-	promInfohashesCount.Add(delta)
-}
-
 // ErrInvalidGCInterval is returned for a GarbageCollectionInterval that is
 // less than or equal to zero.
 var ErrInvalidGCInterval = errors.New("invalid garbage collection interval")
 
 // Config holds the configuration of a memory PeerStore.
 type Config struct {
-	GarbageCollectionInterval time.Duration `yaml:"gc_interval"`
-	PeerLifetime              time.Duration `yaml:"peer_lifetime"`
-	ShardCount                int           `yaml:"shard_count"`
+	GarbageCollectionInterval   time.Duration `yaml:"gc_interval"`
+	PrometheusReportingInterval time.Duration `yaml:"prometheus_reporting_interval"`
+	PeerLifetime                time.Duration `yaml:"peer_lifetime"`
+	ShardCount                  int           `yaml:"shard_count"`
 }
 
 // LogFields renders the current config as a set of Logrus fields.
@@ -108,10 +115,6 @@ func New(cfg Config) (storage.PeerStore, error) {
 			select {
 			case <-ps.closing:
 				t.Stop()
-				select {
-				case <-t.C:
-				default:
-				}
 				return
 			case now := <-t.C:
 				ps.setClock(now.UnixNano())
@@ -119,13 +122,32 @@ func New(cfg Config) (storage.PeerStore, error) {
 		}
 	}()
 
+	ps.wg.Add(1)
+	go func() {
+		defer ps.wg.Done()
+		t := time.NewTicker(cfg.PrometheusReportingInterval)
+		for {
+			select {
+			case <-ps.closing:
+				t.Stop()
+				return
+			case <-t.C:
+				before := time.Now()
+				ps.populateProm()
+				log.Debugf("memory: populateProm() took %s", time.Since(before))
+			}
+		}
+	}()
+
 	return ps, nil
 }
 
 type serializedPeer string
 
 type peerShard struct {
-	swarms map[bittorrent.InfoHash]swarm
+	swarms      map[bittorrent.InfoHash]swarm
+	numSeeders  uint64
+	numLeechers uint64
 	sync.RWMutex
 }
 
@@ -144,6 +166,24 @@ type peerStore struct {
 	wg    sync.WaitGroup
 }
 
+// populateProm aggregates metrics over all shards and then posts them to
+// prometheus.
+func (ps *peerStore) populateProm() {
+	var numInfohashes, numSeeders, numLeechers uint64
+
+	for _, s := range ps.shards {
+		s.RLock()
+		numInfohashes += uint64(len(s.swarms))
+		numSeeders += s.numSeeders
+		numLeechers += s.numLeechers
+		s.RUnlock()
+	}
+
+	promInfohashesCount.Set(float64(numInfohashes))
+	promSeedersCount.Set(float64(numSeeders))
+	promLeechersCount.Set(float64(numLeechers))
+}
+
 var _ storage.PeerStore = &peerStore{}
 
 func (ps *peerStore) getClock() int64 {
@@ -209,9 +249,12 @@ func (ps *peerStore) PutSeeder(ih bittorrent.InfoHash, p bittorrent.Peer) error
 			seeders:  make(map[serializedPeer]int64),
 			leechers: make(map[serializedPeer]int64),
 		}
-		recordInfohashesDelta(1)
 	}
 
+	if _, ok := shard.swarms[ih].seeders[pk]; !ok {
+		// new peer
+		shard.numSeeders++
+	}
 	shard.swarms[ih].seeders[pk] = ps.getClock()
 
 	shard.Unlock()
@@ -240,11 +283,14 @@ func (ps *peerStore) DeleteSeeder(ih bittorrent.InfoHash, p bittorrent.Peer) err
 		return storage.ErrResourceDoesNotExist
 	}
 
-	delete(shard.swarms[ih].seeders, pk)
+	if _, ok := shard.swarms[ih].seeders[pk]; ok {
+		// seeder actually removed
+		shard.numSeeders--
+		delete(shard.swarms[ih].seeders, pk)
+	}
 
 	if len(shard.swarms[ih].seeders)|len(shard.swarms[ih].leechers) == 0 {
 		delete(shard.swarms, ih)
-		recordInfohashesDelta(-1)
 	}
 
 	shard.Unlock()
@@ -268,9 +314,12 @@ func (ps *peerStore) PutLeecher(ih bittorrent.InfoHash, p bittorrent.Peer) error
 			seeders:  make(map[serializedPeer]int64),
 			leechers: make(map[serializedPeer]int64),
 		}
-		recordInfohashesDelta(1)
 	}
 
+	if _, ok := shard.swarms[ih].leechers[pk]; !ok {
+		// new leecher
+		shard.numLeechers++
+	}
 	shard.swarms[ih].leechers[pk] = ps.getClock()
 
 	shard.Unlock()
@@ -299,11 +348,14 @@ func (ps *peerStore) DeleteLeecher(ih bittorrent.InfoHash, p bittorrent.Peer) er
 		return storage.ErrResourceDoesNotExist
 	}
 
-	delete(shard.swarms[ih].leechers, pk)
+	if _, ok := shard.swarms[ih].leechers[pk]; ok {
+		// leecher actually removed
+		shard.numLeechers--
+		delete(shard.swarms[ih].leechers, pk)
+	}
 
 	if len(shard.swarms[ih].seeders)|len(shard.swarms[ih].leechers) == 0 {
 		delete(shard.swarms, ih)
-		recordInfohashesDelta(-1)
 	}
 
 	shard.Unlock()
@@ -327,11 +379,18 @@ func (ps *peerStore) GraduateLeecher(ih bittorrent.InfoHash, p bittorrent.Peer)
 			seeders:  make(map[serializedPeer]int64),
 			leechers: make(map[serializedPeer]int64),
 		}
-		recordInfohashesDelta(1)
 	}
 
-	delete(shard.swarms[ih].leechers, pk)
+	if _, ok := shard.swarms[ih].leechers[pk]; ok {
+		// leecher actually removed
+		shard.numLeechers--
+		delete(shard.swarms[ih].leechers, pk)
+	}
 
+	if _, ok := shard.swarms[ih].seeders[pk]; !ok {
+		// new seeder
+		shard.numSeeders++
+	}
 	shard.swarms[ih].seeders[pk] = ps.getClock()
 
 	shard.Unlock()
@@ -435,7 +494,6 @@ func (ps *peerStore) collectGarbage(cutoff time.Time) error {
 	default:
 	}
 
-	var ihDelta float64
 	cutoffUnix := cutoff.UnixNano()
 	start := time.Now()
 	for _, shard := range ps.shards {
@@ -459,18 +517,19 @@ func (ps *peerStore) collectGarbage(cutoff time.Time) error {
 			for pk, mtime := range shard.swarms[ih].leechers {
 				if mtime <= cutoffUnix {
 					delete(shard.swarms[ih].leechers, pk)
+					shard.numLeechers--
 				}
 			}
 
 			for pk, mtime := range shard.swarms[ih].seeders {
 				if mtime <= cutoffUnix {
 					delete(shard.swarms[ih].seeders, pk)
+					shard.numSeeders--
 				}
 			}
 
 			if len(shard.swarms[ih].seeders)|len(shard.swarms[ih].leechers) == 0 {
 				delete(shard.swarms, ih)
-				ihDelta--
 			}
 
 			shard.Unlock()
@@ -481,7 +540,6 @@ func (ps *peerStore) collectGarbage(cutoff time.Time) error {
 	}
 
 	recordGCDuration(time.Since(start))
-	recordInfohashesDelta(ihDelta)
 
 	return nil
 }
diff --git a/storage/memory/peer_store_test.go b/storage/memory/peer_store_test.go
index f2478b1..c7b9354 100644
--- a/storage/memory/peer_store_test.go
+++ b/storage/memory/peer_store_test.go
@@ -9,7 +9,7 @@ import (
 )
 
 func createNew() s.PeerStore {
-	ps, err := New(Config{ShardCount: 1024, GarbageCollectionInterval: 10 * time.Minute})
+	ps, err := New(Config{ShardCount: 1024, GarbageCollectionInterval: 10 * time.Minute, PrometheusReportingInterval: 10 * time.Minute})
 	if err != nil {
 		panic(err)
 	}