diff --git a/client.go b/client.go
index 85b27923..034b1bc3 100644
--- a/client.go
+++ b/client.go
@@ -2562,6 +2562,15 @@ func (cli *Client) ReportRoom(ctx context.Context, roomID id.RoomID, reason stri
 	return err
 }
 
+// AdminWhoIs fetches session information belonging to a specific user. Typically requires being a server admin.
+//
+// https://spec.matrix.org/v1.15/client-server-api/#get_matrixclientv3adminwhoisuserid
+func (cli *Client) AdminWhoIs(ctx context.Context, userID id.UserID) (resp RespWhoIs, err error) {
+	urlPath := cli.BuildClientURL("v3", "admin", "whois", userID)
+	_, err = cli.MakeRequest(ctx, http.MethodGet, urlPath, nil, &resp)
+	return
+}
+
 // UnstableGetSuspendedStatus uses MSC4323 to check if a user is suspended.
 func (cli *Client) UnstableGetSuspendedStatus(ctx context.Context, userID id.UserID) (res *RespSuspended, err error) {
 	urlPath := cli.BuildClientURL("unstable", "uk.timedout.msc4323", "admin", "suspend", userID)
diff --git a/responses.go b/responses.go
index 8ab78373..ae41084e 100644
--- a/responses.go
+++ b/responses.go
@@ -715,3 +715,23 @@ type RespSuspended struct {
 type RespLocked struct {
 	Locked bool `json:"locked"`
 }
+
+type ConnectionInfo struct {
+	IP        string             `json:"ip,omitempty"`
+	LastSeen  jsontime.UnixMilli `json:"last_seen,omitempty"`
+	UserAgent string             `json:"user_agent,omitempty"`
+}
+
+type SessionInfo struct {
+	Connections []ConnectionInfo `json:"connections,omitempty"`
+}
+
+type DeviceInfo struct {
+	Sessions []SessionInfo `json:"sessions,omitempty"`
+}
+
+// RespWhoIs is the response body for https://spec.matrix.org/v1.15/client-server-api/#get_matrixclientv3adminwhoisuserid
+type RespWhoIs struct {
+	UserID  id.UserID                `json:"user_id,omitempty"`
+	Devices map[id.Device]DeviceInfo `json:"devices,omitempty"`
+}