A 46-year-old man, without remarkable past medical history, had a perianal ulcer that appeared spontaneously two months before presentation. At admission, the ulcer was painless, measuring 4 to 5 cm in diameter and showing detachment and a slightly papillomatous aspect at the edge but without induration of the base. Microscopic examination revealed cutaneous ulceration with a well-developed inflammatory response, a few small vessels with intraluminal thrombosis or necrotizing walls, and isolated microscopic granulomata. No infectious disease was detected. The diagnosis of Wegener's granulomatosis was made six months later, when the disease was clinically evident in three principal sites: upper airways, lung, and kidney. At that time, serum antineutrophil cytoplasmic autoantibodies were detected with indirect immunofluorescence microscopy. There has been an excellent response to immunosuppressive therapy. Review of the literature revealed no similar reports.