Computed tomography (CT) is increasingly used to evaluate abdominal diseases, including those of the colon. Recent CT studies have documented colonic abnormalities in patients with pseudomembranous colitis; however, these, findings are not widely appreciated by primary care physicians. Over a 25-month period, we prospectively identified 13 patients who had proven pseudomembranous colitis evaluated by abdominal CT. The primary indications for CT were abdominal pain with or without fever in 9 patients, fever of unknown origin in 1, evaluation of other abdominal processes in 1, and as part of this study after documentation of pseudomembranous colitis in 2. Importantly, the diagnosis of pseudomembranous colitis was first considered on the basis of the CT findings in 9 patients with abdominal pain or fever. Diffuse thickening of the colonic wall, ranging from 4 to 40 mm, was the most common radiologic finding, seen in 8 patients (62%). In 3 cases, wall thickening was seen in the descending colon and rectosigmoid, with one of these also having a thickened transverse colon. Colonic wall thickening, which may be dramatic, appears to be an almost uniform accompaniment of pseudomembranous colitis and may be present without clinically severe disease. These CT findings in the appropriate clinical setting should suggest colitis due to Clostridmm difficile and prompt the appropriate evaluation for this disease. © 1995 Southern Medical Association.