Necrotizing infections of soft tissues are rapidly progressive infections accompanied by a high mortality. Clinical presentation involves fever, cellulitis, edema, crepitus, bullae, necrosis and sepsis. Operative findings include fascial and subcutaneous tissue necrosis with or without myonecrosis. The treatment is prompt surgical debridement. Delay in treatment results in decreased survival time. The mortality in our study was 30 per cent (20 of 33). The time from recognition of an infection by the patient or physician until operative debridement averaged three and one-half days for survivors compared with 11.7 days for nonsurvivors. These infections frequently occur in compromised hosts and the mortality is greatly increased in these patients. Patients with diabetes had a mortality of 63 per cent (five of eight). The mortality for infections of the abdomen (44 per cent) and perineum (38 per cent) is greater than for the extremities (18 per cent). The bacteriologic findings of these infections involved three combinations of organisms. We had 30 mixed infections involving two or more organisms. In addition, three patients had identical signs and symptoms caused by infection with a single organism--Vibrio species. These patients all had some type of contact with a marine environment as a predisposing cause. We also applied both the APACHE and SIS systems to these patients to evaluate the severity of the illness. Nonsurvivors presented with a mean SIS score of 8.64 compared with survivors with 3.82. Initial scores with the APACHE system for nonsurvivors was 12.0 compared with 2.14 for survivors. In both systems, scores rapidly increased at three and seven days in nonsurvivors as compared with a rapid decline in the survivors. We suggest that the best descriptive system is to simply identify the organisms and tissues involved.