Recent treatment of young patients (aged 40 years or less) with complicated diverticulitis prompted us to review our experience. During a 9-year period ending in December 1990, 61 of 238 patients treated for acute diverticulitis were 40 years of age or younger. The younger patients were primarily obese Hispanic males in whom the correct diagnosis was frequently missed. Younger patients more frequently required an operation on an urgent basis for complications of diverticulitis during the initial hospitalization. The most common indication for operation in young patients was perforation compared with recurrent disease for the older age group. The younger group had a sevenfold incidence of enteric fistulas complicating their acute episode of diverticulitis. Our data suggest that diverticular disease in young patients is more common and more likely to require early surgical intervention than previously noted. In addition, obesity may represent an important etiologic factor in the development of diverticular disease.