Gas formation within the soft tissue is a manifestation of infection. Gas gangrene is a bacterial infection caused by several clostridial species associated with high morbidity and mortality. The infection usually follows open contaminated wounds with concomitant vascular compromise. Another form of clostridial infection is anaerobic cellulitis where the gas is confined to the subcutaneous and superficial fascial layers. Diabetes mellitus, steroid treatment, and immunodeficiency states including HIV infection are predisposing factors. Amputation is usually necessary to control infection and prevent death.