The aim of this study was to examine any association between the presence of diabetes in patients with gas gangrene of the legs and mortality following major lower limb amputation. In a retrospective study, patients submitted to amputation of lower limbs for anaerobic infections were evaluated in the period from January 2005 to January 2007 in the University Hospital de Base in Sao Jose do Rio Preto. All the patients were hospitalized for the treatment of ulcerated lesions of the leg. The study sample consisted of 30 men and 10 women aged between 46 and 87 years (mean 69 years) suffering from anaerobic infections. During treatment, the presence of crepitation in the skin was observed as was gas by radiological examination. Amputation was performed within 2 to 6 hours after diagnosis. Diabetes was identified in 33 patients and death occurred within the perioperative period in 12 cases. Diabetes is associated with the necessity of amputation for gas gangrene resulting in a high mortality rate.