A 63-year-old Chinese man was admitted to the emergency department with severe pain over the right lower quadrant (RLQ) of abdomen and perineum of 1-day's duration. He had a significant history of diabetes mellitus. Abdominal palpation revealed tenderness with subcutaneous crepitus over the RLQ of abdominal wall. Perineal skin showed erythematous swelling. Fournier's gangrene with retroperitoneal invasion was suspected from the pattern of KUB, and computed tomography of the pelvis demonstrated the extent of infectious process. Operative findings during surgical debridement showed necrotizing myofasciitis over the abdominal wall, right thigh scrotum and perineum with retroperitoneal invasion. The case presented here should increase physicians' awareness of the condition of Fournier' gangrene which may present with acute abdomen and the physician must have a high index of suspicion in a high risk patient with vague perineal complaints.