The records of 133 consecutive patients (65 men, 68 women; age range, 15 months to 88 years; median, 57 years) with either a positive Clostridium difficile stool culture or toxin assay from 1982 to 1984 were reviewed in order to assess the pattern of this disease in a large hospital and to examine the type of patient at risk. All patients had diarrhea and/or bloody stools (121 and 36, respectively). Less specific symptoms were common. Most patients had been exposed to multiple antibiotics, but of those who had received only one agent, cephalosporins were most common (21/43). Nineteen patients had cancer chemotherapy. C. difficile toxin assay was positive in 106, culture was positive in 74, and pseudomembranes were seen in six of the 39 patients who underwent endoscopy. Treatment consisted of stopping antibiotic therapy alone (86 percent response), oral vancomycin (88 percent response) or metronidazole (82 percent response). The overall mortality rate was 23 percent, due to C. difficile colitis in three of 31 cases. Many patients were receiving medications or had other diseases associated with fecal stasis. There is much circumstantial evidence to support a role for fecal stasis in the pathogenesis of C. difficile disease. Patients predisposed to colonic stasis who are receiving antibiotics should be considered at risk for this disease, and preventative measures should be taken to decrease stool transit times.