Mixed connective tissue disease is a syndrome having clinical features of scleroderma, systemic lupus erythematosus, and polymyositis with a unique combination of clinical and laboratory findings. Not all patients with clinical features of more than one connective tissue disease fit the mixed connective disorders category; therefore, the term "overlap syndrome" is applied to patients with features of two or more connective tissue diseases. Gastrointestinal involvement in progressive systemic sclerosis is common, with the esophagus being the usual site, followed by the small bowel, colon, and stomach. Colonic involvement is reported to occur in 10 to 50 percent of cases and is typically manifested radiographically as wide-mouthed diverticular saculations. Symptoms secondary to colonic involvement are rare but occasionally serious, such as impaction of barium or feces. A case is described in which systemic lupus erythematosus coexisted with previously undiagnosed scleroderma involving predominantly the gastrointestinal tract and resulting in megacolon.