We present the first five reported cases of Clostridium difficile-associated diarrhea (CDAD) in children with infant botulism caused by Clostridium botulinum. We compare two fulminant cases of colitis in children with colonic stasis, the first caused by infant botulism and the second caused by Hirschsprung's disease. In both children, colitis was accompanied by hypovolemia, hypotension, profuse ascites, pulmonary effusion, restrictive pulmonary disease, and femoral-caval thrombosis. Laboratory findings included pronounced leukocytosis, hypoalbuminemia, hyponatremia, coagulopathy, and, when examined in the child with infant botulism, detection of C. difficile toxin in ascites. CDAD recurred in both children, even though difficile cytotoxin was undetectable in stool after prolonged initial therapy. Four children who had both infant botulism and milder CDAD also are described. Colonic stasis, whether acquired, as in infant botulism, or congenital, as in Hirschsprung's disease, may contribute to the susceptibility to and the severity of CDAD.