We describe a case of gas-producing infection following a perianal abscess. A 61-year-old man was admitted to our hospital complaining of perineal pain and was found to have a perianal abscess. He was diabetic but had not received treatment for the disease. Although the perianal abscess was drained and antibiotic treatment started, severe swelling of the scrotum, with crepitation, redness, and partial necrosis progressed rapidly. Computed tomography revealed subcutaneous gas formation in the scrotum. A culture study revealed Clostridium, Enterococcus, and numerous other types of bacteria. The patient was diagnosed with Fournier's gangrene caused by infection with Clostridium in combination with other species of bacteria. The infection was refractory to drainage and antibiotic therapy. Thus, repeated extensive debridement of all necrotic tissue in the scrotum was required until healthy granulation was present in the wound. Our case shows that, in patients with Fournier's gangrene caused by infection with Clostridium in combination with other species of bacteria, the mainstay of treatment should be open drainage and aggressive surgical debridement of all necrotic tissue, followed by broad-spectrum antibiotic therapy.