Klippel-Trenaunay-Weber syndrome (KTS) is an unusual congenital anomaly characterized by cutaneous hemangiomas, varicosities and bony hypertrophy of the extremities. Herein the case is reported of a 24-year-old man with urethral bleeding from hemangiomas associated with KTS that were successfully managed by endoscopic sclerotherapy. A 23-G puncture needle was inserted into the bleeding vein to inject a 5% solution of monoethanolamine oleate (Oldamine), which is typically used for sclerotherapy of esophageal vasix. At a 4-month follow-up, the patient only had slightly bloodstained urethral discharge, and is doing well. This is the first case reporting endoscopic sclerotherapy for a KTS-associated urethral hemangioma.