This analysis of our experience with 57 men with necrotizing fasciitis of the genitalia was done to identify prognostic variables and to assess the results of a treatment policy of immediate and, if required, repetitive surgical debridements. The mean age of the patients was 55 years. Thirty-eight patients were alcoholics or diabetics, or both. All of the infections were of a genitourinary, anorectal or cutaneous source. Thirty-five per cent of the infections were confined to the genitalia and 65 per cent extended to the abdominal wall or thigh, or both. Forty-seven patients survived. Survival was associated significantly with a younger age, a serum blood urea nitrogen (BUN) level of less than 50 milligrams per deciliter at presentation, the absence of a constellation of abnormalities at presentation consistent with sepsis and a decreased incidence of major complications after initial débridement (p less than 0.05 to 0.01). Survival was not associated with the extent of infection, the duration of symptoms before hospitalization, systemic risk factors, the source of infection, abnormal findings at presentation (excluding a BUN of greater than 50 milligrams per deciliter) and the bacteriologic factors of the infection. Both localized and extensive necrotizing fasciitis of the male genitalia are potentially lethal disorders that require prompt treatment.