Twenty-eight patients with necrotizing fasciitis of the perineum were treated at the Mount Sinai Medical Center from 1971 to 1979. Ten of the 28 died of the disease, for a mortality rate of 36%. The mortality rate was even higher when the lesion was located in the perianal area and associated with diabetes mellitus and delayed surgical intervention. Necrotizing fasciitis is a rare disease that involves both superficial and deep fascia. It begins with fascial necrosis at onset and rapidly progresses to surrounding fascial planes, eventually involving overlying skin and underlying muscle. Evidence proves that it is not the result of abscess, but primarily originates from fascia and is devoid of frank pus in the well-formed pyogenic abscess cavity. If one observes dark brown necrotic turbid fluid and fails to see frank pus, the disease should be treated as necrotizing fasciitis by complete surgical removal of all necrotic tissue until the normal plane is reached.