This uncommon, severe infection involves the subcutaneous soft tissues, including the superficial and deep fascial layers, with early sparing of the skin and late involvement of the muscle. It is most commonly seen in the lower extremities, abdominal wall, perianal and groin area, and postoperative wounds, but can manifest in any body part. The infection is usually spread from a site of trauma or surgical wound, abscess, decubitus ulcer, or intestinal perforation. Alcoholism, parenteral drug abuse, and diabetes mellitus are predisposing factors. Pain, tenderness, erythema, swelling, warmth, shiny skin, lymphangitis, and lymphadenitis are early clinical findings. Later, there is rapid progression with changes in skin color, formation of bullae with clear pink or purple fluid and cutaneous necrosis within 48 hours. The skin becomes anesthetic and subcutaneous gas may be present. Systemic toxicity may be manifest by fever, dehydration, leukocytosis, and frequently positive blood cultures. Two groups of organisms are implicated in necrotizing fasciitis. Type I includes anaerobic species (Bacteroides and Peptostreptococcus) and type II group A streptococci alone or with Staphylococcus aureus. The differential diagnosis includes cellulitis, osteomyelitis, gas gangrene, streptococcal myonecrosis, infected vascular gangrene, and trauma.