diff --git a/cli/silence.go b/cli/silence.go
index 494126f3..c0b16e45 100644
--- a/cli/silence.go
+++ b/cli/silence.go
@@ -32,4 +32,5 @@ func init() {
 	silenceCmd.AddCommand(expireCmd)
 	silenceCmd.AddCommand(queryCmd)
 	silenceCmd.AddCommand(importCmd)
+	silenceCmd.AddCommand(updateCmd)
 }
diff --git a/cli/silence_update.go b/cli/silence_update.go
new file mode 100644
index 00000000..46c765a6
--- /dev/null
+++ b/cli/silence_update.go
@@ -0,0 +1,147 @@
+package cli
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"path"
+	"time"
+
+	"github.com/prometheus/alertmanager/cli/format"
+	"github.com/prometheus/alertmanager/types"
+	"github.com/spf13/cobra"
+	flag "github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+type getResponse struct {
+	Status    string        `json:"status"`
+	Data      types.Silence `json:"data,omitempty"`
+	ErrorType string        `json:"errorType,omitempty"`
+	Error     string        `json:"error,omitempty"`
+}
+
+var updateFlags *flag.FlagSet
+var updateCmd = &cobra.Command{
+	Use:     "update <id> ...",
+	Aliases: []string{"extend"},
+	Args:    cobra.MinimumNArgs(1),
+	Short:   "Update silences",
+	Long:    `Extend or update existing silence in Alertmanager.`,
+	Run:     CommandWrapper(update),
+}
+
+func init() {
+	updateCmd.Flags().StringP("expires", "e", "", "Duration of silence (100h)")
+	updateCmd.Flags().String("expire-on", "", "Expire at a certain time (Overwrites expires) RFC3339 format 2006-01-02T15:04:05Z07:00")
+	updateCmd.Flags().StringP("comment", "c", "", "A comment to help describe the silence")
+	updateFlags = updateCmd.Flags()
+}
+
+func update(cmd *cobra.Command, args []string) error {
+	if len(args) < 1 {
+		return fmt.Errorf("no silence IDs specified")
+	}
+
+	alertmanagerUrl, err := GetAlertmanagerURL()
+	if err != nil {
+		return err
+	}
+
+	var updatedSilences []types.Silence
+	for _, silenceId := range args {
+		silence, err := getSilenceById(silenceId, *alertmanagerUrl)
+		if err != nil {
+			return err
+		}
+		silence, err = updateSilence(silence)
+		if err != nil {
+			return err
+		}
+		updatedSilences = append(updatedSilences, *silence)
+	}
+
+	quiet := viper.GetBool("quiet")
+	if quiet {
+		for _, silence := range updatedSilences {
+			fmt.Println(silence.ID)
+		}
+	} else {
+		formatter, found := format.Formatters[viper.GetString("output")]
+		if !found {
+			return fmt.Errorf("unknown output formatter")
+		}
+		formatter.FormatSilences(updatedSilences)
+	}
+	return nil
+}
+
+// This takes an url.URL and not a pointer as we will modify it for our API call.
+func getSilenceById(silenceId string, baseUrl url.URL) (*types.Silence, error) {
+	baseUrl.Path = path.Join(baseUrl.Path, "/api/v1/silence", silenceId)
+	res, err := http.Get(baseUrl.String())
+	if err != nil {
+		return nil, err
+	}
+
+	defer res.Body.Close()
+	body, err := ioutil.ReadAll(res.Body)
+	if err != nil {
+		return nil, fmt.Errorf("couldn't read response body: %v", err)
+	}
+
+	if res.StatusCode == 404 {
+		return nil, fmt.Errorf("no silence found with id: %v", silenceId)
+	}
+	if res.StatusCode != 200 {
+		return nil, fmt.Errorf("received %d response from Alertmanager: %v", res.StatusCode, body)
+	}
+
+	var response getResponse
+	err = json.Unmarshal(body, &response)
+	return &response.Data, nil
+}
+
+func updateSilence(silence *types.Silence) (*types.Silence, error) {
+	if updateFlags.Changed("expires") {
+		expires, err := updateFlags.GetString("expires")
+		if err != nil {
+			return nil, err
+		}
+		duration, err := time.ParseDuration(expires)
+		if err != nil {
+			return nil, err
+		}
+		silence.EndsAt = time.Now().UTC().Add(duration)
+	}
+
+	// expire-on will override expires value if both are specified
+	if updateFlags.Changed("expire-on") {
+		expireOn, err := updateFlags.GetString("expire-on")
+		if err != nil {
+			return nil, err
+		}
+		endsAt, err := time.Parse(time.RFC3339, expireOn)
+		if err != nil {
+			return nil, err
+		}
+		silence.EndsAt = endsAt
+	}
+
+	if updateFlags.Changed("comment") {
+		comment, err := updateFlags.GetString("comment")
+		if err != nil {
+			return nil, err
+		}
+		silence.Comment = comment
+	}
+
+	// addSilence can also be used to update an existing silence
+	_, err := addSilence(silence)
+	if err != nil {
+		return nil, err
+	}
+	return silence, nil
+}