PURPOSE: To establish the guidelines for the differential diagnosis and proper initial treatment of the gas forming infections through the review of literature and our clinical experiences. MATERIALS AND METHODS: The radiological findings, clinical course, gram stain, bacterial culture, predisposing factors and treatment of four cases of gas forming infections from January 1994 to August 2001, were retrospectively analyzed. RESULTS: Three cases diagnosed presumptively as gas gangrene were improved through amputation or disarticulation and intravenous antibiotics. One case diagnosed presumptively as non-clostridial infection was expired due to sepsis in spite of incision, drainage and intravenous antibiotics. In the bacterial culture, two cases were non-clostridial infection, one case was not able to diagnose and one case was clostridial myonecrosis(gas gangrene) CONCLUSION: The gas forming infections are rare but life-threatening. When the proper initial treatment is delayed, the fatal complications may result. So, the presumptive diagnosis through gram stain, clinical course, radiological findings should be made as soon as possible, and according to which, the appropriate initial treatment, such as, surgical debridement, amputation, intravenous antibiotics must be started. The following treatments should be corrected by definitive diagnosis through the bacterial culture.