diff --git a/codec.go b/codec.go
index 9fef2da..64e7d04 100644
--- a/codec.go
+++ b/codec.go
@@ -1,6 +1,7 @@
 package multiaddr
 
 import (
+	"encoding/base32"
 	"encoding/binary"
 	"errors"
 	"fmt"
@@ -165,6 +166,40 @@ func addressStringToBytes(p Protocol, s string) ([]byte, error) {
 		binary.BigEndian.PutUint16(b, uint16(i))
 		return b, nil
 
+	case P_ONION:
+		addr := strings.Split(s, ":")
+		if len(addr) != 2 {
+			return nil, fmt.Errorf("failed to parse %s addr: %s does not contain a port number.", p.Name, s)
+		}
+
+		// onion address without the ".onion" substring
+		if len(addr[0]) != 16 {
+			return nil, fmt.Errorf("failed to parse %s addr: %s not a Tor onion address.", p.Name, s)
+		}
+		onionHostBytes, err := base32.StdEncoding.DecodeString(strings.ToUpper(addr[0]))
+		if err != nil {
+			return nil, fmt.Errorf("failed to decode base32 %s addr: %s %s", p.Name, s, err)
+		}
+
+		// onion port number
+		i, err := strconv.Atoi(addr[1])
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse %s addr: %s", p.Name, err)
+		}
+		if i >= 65536 {
+			return nil, fmt.Errorf("failed to parse %s addr: %s", p.Name, "port greater than 65536")
+		}
+		if i < 1 {
+			return nil, fmt.Errorf("failed to parse %s addr: %s", p.Name, "port less than 1")
+		}
+
+		onionPortBytes := make([]byte, 2)
+		binary.BigEndian.PutUint16(onionPortBytes, uint16(i))
+		bytes := []byte{}
+		bytes = append(bytes, onionHostBytes...)
+		bytes = append(bytes, onionPortBytes...)
+		return bytes, nil
+
 	case P_IPFS: // ipfs
 		// the address is a varint prefixed multihash string representation
 		m, err := mh.FromB58String(s)
diff --git a/multiaddr_test.go b/multiaddr_test.go
index f0e9c36..3a60751 100644
--- a/multiaddr_test.go
+++ b/multiaddr_test.go
@@ -25,6 +25,12 @@ func TestConstructFails(t *testing.T) {
 		"/sctp",
 		"/udp/65536",
 		"/tcp/65536",
+		"/onion/9imaq4ygg2iegci7:80",
+		"/onion/aaimaq4ygg2iegci7:80",
+		"/onion/timaq4ygg2iegci7:0",
+		"/onion/timaq4ygg2iegci7:-1",
+		"/onion/timaq4ygg2iegci7",
+		"/onion/timaq4ygg2iegci@:666",
 		"/udp/1234/sctp",
 		"/udp/1234/udt/1234",
 		"/udp/1234/utp/1234",
@@ -49,6 +55,8 @@ func TestConstructSucceeds(t *testing.T) {
 		"/ip4/0.0.0.0",
 		"/ip6/::1",
 		"/ip6/2601:9:4f81:9700:803e:ca65:66e8:c21",
+		"/onion/timaq4ygg2iegci7:1234",
+		"/onion/timaq4ygg2iegci7:80/http",
 		"/udp/0",
 		"/tcp/0",
 		"/sctp/0",
diff --git a/protocols.csv b/protocols.csv
index 213e9b5..fa27ba3 100644
--- a/protocols.csv
+++ b/protocols.csv
@@ -10,3 +10,4 @@ code	size	name
 421	V	ipfs
 480	0	http
 443	0	https
+444	10	onion
\ No newline at end of file
diff --git a/protocols.go b/protocols.go
index c4ee5df..c233cef 100644
--- a/protocols.go
+++ b/protocols.go
@@ -30,6 +30,7 @@ const (
 	P_IPFS  = 421
 	P_HTTP  = 480
 	P_HTTPS = 443
+	P_ONION = 444
 )
 
 // These are special sizes
@@ -46,6 +47,7 @@ var Protocols = []Protocol{
 	Protocol{P_IP6, 128, "ip6", CodeToVarint(P_IP6)},
 	// these require varint:
 	Protocol{P_SCTP, 16, "sctp", CodeToVarint(P_SCTP)},
+	Protocol{P_ONION, 80, "onion", CodeToVarint(P_ONION)},
 	Protocol{P_UTP, 0, "utp", CodeToVarint(P_UTP)},
 	Protocol{P_UDT, 0, "udt", CodeToVarint(P_UDT)},
 	Protocol{P_HTTP, 0, "http", CodeToVarint(P_HTTP)},