diff --git a/client.go b/client.go
index 5236053..29a890a 100644
--- a/client.go
+++ b/client.go
@@ -256,9 +256,10 @@ func clientRequestBuildReq(c *Client, req *sip.Request) error {
 	// https://www.rfc-editor.org/rfc/rfc3261#section-8.1.1
 	// A valid SIP request formulated by a UAC MUST, at a minimum, contain
 	// the following header fields: To, From, CSeq, Call-ID, Max-Forwards,
-	// and Via;
+	// Via, and User-Agent;
+
+	mustHeader := make([]sip.Header, 0, 7)
 
-	mustHeader := make([]sip.Header, 0, 6)
 	if v := req.Via(); v == nil {
 		// Multi VIA value must be manually added
 		via := clientRequestCreateVia(c, req)
@@ -313,6 +314,13 @@ func clientRequestBuildReq(c *Client, req *sip.Request) error {
 
 	}
 
+	if v := req.UserAgent(); v == nil {
+
+		useragent := sip.UserAgentHeader(c.UserAgent.uaHeader)
+		mustHeader = append(mustHeader, &useragent)
+
+	}
+
 	if v := req.CSeq(); v == nil {
 		cseq := sip.CSeqHeader{
 			SeqNo:      1,
diff --git a/example/proxysip/go.mod b/example/proxysip/go.mod
index 9504534..236ad9a 100644
--- a/example/proxysip/go.mod
+++ b/example/proxysip/go.mod
@@ -8,7 +8,7 @@ require (
 	github.com/arl/statsviz v0.6.0
 	github.com/emiago/sipgo v0.23.1-0.20240913054121-597f4c4406dd
 	github.com/prometheus/client_golang v1.17.0
-	github.com/rs/zerolog v1.32.0
+	github.com/rs/zerolog v1.33.0
 	github.com/sirupsen/logrus v1.9.3
 	github.com/stretchr/testify v1.9.0
 )
@@ -33,7 +33,7 @@ require (
 	github.com/prometheus/common v0.44.0 // indirect
 	github.com/prometheus/procfs v0.11.1 // indirect
 	github.com/satori/go.uuid v1.2.1-0.20181028125025-b2ce2384e17b // indirect
-	golang.org/x/sys v0.19.0 // indirect
+	golang.org/x/sys v0.24.0 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
diff --git a/example/proxysip/go.sum b/example/proxysip/go.sum
index ed1362b..f50d786 100644
--- a/example/proxysip/go.sum
+++ b/example/proxysip/go.sum
@@ -59,6 +59,7 @@ github.com/rogpeppe/go-internal v1.11.0/go.mod h1:ddIwULY96R17DhadqLgMfk9H9tvdUz
 github.com/rs/xid v1.5.0/go.mod h1:trrq9SKmegXys3aeAKXMUTdJsYXVwGY3RLcfgqegfbg=
 github.com/rs/zerolog v1.32.0 h1:keLypqrlIjaFsbmJOBdB/qvyF8KEtCWHwobLp5l/mQ0=
 github.com/rs/zerolog v1.32.0/go.mod h1:/7mN4D5sKwJLZQ2b/znpjC3/GQWY/xaDXUM0kKWRHss=
+github.com/rs/zerolog v1.33.0/go.mod h1:/7mN4D5sKwJLZQ2b/znpjC3/GQWY/xaDXUM0kKWRHss=
 github.com/satori/go.uuid v1.2.1-0.20181028125025-b2ce2384e17b h1:gQZ0qzfKHQIybLANtM3mBXNUtOfsCFXeTsnBqCsx1KM=
 github.com/satori/go.uuid v1.2.1-0.20181028125025-b2ce2384e17b/go.mod h1:dA0hQrYB0VpLJoorglMZABFdXlWrHn1NEOzdhQKdks0=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
@@ -79,6 +80,7 @@ golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.19.0 h1:q5f1RH2jigJ1MoAWp2KTp3gm5zAGFUTarQZ5U386+4o=
 golang.org/x/sys v0.19.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.24.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/tools v0.0.0-20190624222133-a101b041ded4/go.mod h1:/rFqwRUd4F7ZHNgwSSTFct+R/Kf4OFW1sUzUTQQTgfc=
 golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
diff --git a/sip/headers.go b/sip/headers.go
index d6d09e4..a95a1ed 100644
--- a/sip/headers.go
+++ b/sip/headers.go
@@ -51,6 +51,8 @@ type headers struct {
 	maxForwards   *MaxForwardsHeader
 	referTo       *ReferToHeader
 	referredBy    *ReferredByHeader
+
+	useragent *UserAgentHeader
 }
 
 func (hs *headers) String() string {
@@ -96,6 +98,8 @@ func (hs *headers) setHeaderRef(header Header) {
 		hs.contentType = m
 	case *MaxForwardsHeader:
 		hs.maxForwards = m
+	case *UserAgentHeader:
+		hs.useragent = m
 	}
 }
 
@@ -123,6 +127,8 @@ func (hs *headers) unref(header Header) {
 		hs.contentType = nil
 	case *MaxForwardsHeader:
 		hs.maxForwards = nil
+	case *UserAgentHeader:
+		hs.useragent = nil
 	}
 }
 
@@ -427,6 +433,17 @@ func (hs *headers) ParseReferredBy() *ReferredByHeader {
 	return nil
 }
 
+// UserAgent returns underlying UserAgent parsed header or nil if not exists
+func (hs *headers) UserAgent() *UserAgentHeader {
+	if hs.useragent == nil {
+		var h UserAgentHeader
+		if parseHeaderLazy(hs, parseUserAgentHeader, []string{"user-agent", "i"}, &h) {
+			hs.useragent = &h
+		}
+	}
+	return hs.useragent
+}
+
 // NewHeader creates generic type of header
 func NewHeader(name, value string) Header {
 	return &genericHeader{
diff --git a/sip/parse_header.go b/sip/parse_header.go
index 4fe4817..9de1788 100644
--- a/sip/parse_header.go
+++ b/sip/parse_header.go
@@ -148,6 +148,16 @@ func parseCallIdHeader(headerText string, callId *CallIDHeader) error {
 	return nil
 }
 
+func parseUserAgentHeader(headerText string, useragent *UserAgentHeader) error {
+	headerText = strings.TrimSpace(headerText)
+	if len(headerText) == 0 {
+		return fmt.Errorf("empty User-Agent body")
+	}
+
+	*useragent = UserAgentHeader(headerText)
+	return nil
+}
+
 func headerParserMaxForwards(headerName string, headerText string) (header Header, err error) {
 	var maxfwd MaxForwardsHeader
 	return &maxfwd, parseMaxForwardsHeader(headerText, &maxfwd)
diff --git a/sip/user_agent_header.go b/sip/user_agent_header.go
new file mode 100644
index 0000000..6c2eaad
--- /dev/null
+++ b/sip/user_agent_header.go
@@ -0,0 +1,33 @@
+package sip
+
+import (
+	"io"
+	"strings"
+)
+
+// UserAgentHeader  is User-Agent header representation.
+type UserAgentHeader string
+
+func (h *UserAgentHeader) String() string {
+	var buffer strings.Builder
+	h.StringWrite(&buffer)
+	return buffer.String()
+}
+
+func (h *UserAgentHeader) StringWrite(buffer io.StringWriter) {
+	buffer.WriteString(h.Name())
+	buffer.WriteString(": ")
+	buffer.WriteString(h.Value())
+}
+
+func (h *UserAgentHeader) Name() string { return "User-Agent" }
+
+func (h *UserAgentHeader) Value() string {
+	if h == nil {
+		return ""
+	} else {
+		return string(*h)
+	}
+}
+
+func (h *UserAgentHeader) headerClone() Header { return h }
diff --git a/ua.go b/ua.go
index 6e2faea..207071d 100644
--- a/ua.go
+++ b/ua.go
@@ -10,6 +10,7 @@ import (
 type UserAgent struct {
 	name        string
 	hostname    string
+	uaHeader    string
 	dnsResolver *net.Resolver
 	tlsConfig   *tls.Config
 	parser      *sip.Parser
@@ -21,9 +22,10 @@ type UserAgentOption func(s *UserAgent) error
 
 // WithUserAgent changes user agent name
 // Default: sipgo
-func WithUserAgent(ua string) UserAgentOption {
+func WithUserAgent(username, uaHeader string) UserAgentOption {
 	return func(s *UserAgent) error {
-		s.name = ua
+		s.name = username
+		s.uaHeader = uaHeader
 		return nil
 	}
 }