We report two cases of gas gangrene developed from sacral pressure sores. The first case was clostridial and the second, non-clostridial gas gangrene. Both patients died within two months. The first patient, a 56-year-old woman suffering from palsy of the lower half of the body for 3 weeks, developed a sacral pressure sore. One month later, crepitus by palpation and gas formation in the X-ray film were detected in the hip and right thigh. A culture of odoriferous pus yielded Clostridium limosum in addition to Staphylococcus intermedius, Enterococcus faecalis, Pseudomonas aeruginosa, and Bacteroides fragilis. Blood culture yielded Bacteroides fragilis. The patient died 50 days after admission in spite of surgical debridement and aggressive therapy with high doses of antibiotics and hyperbaric oxygen. The second patient, a 70-year-old man suffering from diabetic nephropathy, arteriosclerosis obliterans of the lower limbs, and cerebral infarction, developed a large decubitus ulcer covering the whole sacral area. Crepitus and gas were detected in the soft tissue of the left gluteal region. Almost the entire gluteus maximus muscle was necrotic. Bacteroides fragilis, methicillin-resistant or -sensitive Staphylococcus aureus and Escherichia coli were isolated from the muscle. Bacteroides fragilis was also obtained by blood culture. The patient died on the 72nd day after admission.