A 71-year-old man presented with a 6-cm scrotal mass and urinary retention. He had had progressive voiding difficulty after an untreated urethral injury in a traffic accident 15 years before presentation. Retrograde urethrography showed an anterior urethral diverticulum with stone formation. He underwent open diverticulectomy and recovered well. Pathologic examination revealed the diverticulum was lined by granulation tissue. Male urethral diverticula are rare and can be congenital or acquired. An acquired urethral diverticulum, as shown in this case, often results from infection, stricture, or trauma. The diagnosis requires a detailed history, physical examination, imaging studies, and pathologic examination.