Necrotizing fasciitis is a life-threatening soft-tissue infection. It is useful to know the etiology of this disease in each community and region because this information can facilitate early diagnosis and treatment. We reviewed medical records of 217 consecutive patients with necrotizing fasciitis in South Korea. Etiologic organisms were documented in 171 (78.8%) patients. Gram-negative marine bacteria were the most common organisms (68.4%). Seasonal variation in incidence occurred during warmer periods. Liver cirrhosis and alcoholism were common underlying illnesses. Gastrointestinal symptoms were more common in persons infected with gram-negative marine bacteria (56.4% versus 29.6%). Gram-negative bacteria were the predominant pathogens in multiple site involvement. Acute Physiology and Chronic Health Evaluation II scores, marine bacteria, and medical treatment without surgery affected mortality. When necrotic areas included less than three extremities, fasciotomy improved the survival rate. In coastal areas, gram-negative marine bacteria are the most common pathogens associated with necrotizing fasciitis. Fasciotomy can improve survival of patients with necrotic areas that involve less than three sites in necrotizing fasciitis.