We describe a 15-month-old male who presented with fever and diarrhea 24 hr after receiving antibiotics for otitis media. A flexible sigmoidoscopy was initially interpreted endoscopically as antibiotic-associated pseudomembranous colitis, and the patient was treated with vancomycin. The diagnosis of antibiotic-associated colitis was excluded in our patient by the negative stool examination for Clostridium difficile toxin, the failure to obtain supportive features on rectal biopsy, and the failure to demonstrate sigmoidoscopic improvement with vancomycin therapy. Thirteen days later, Y. enterocolitica was cultured from the initial stool specimens. In this case, the raised central whitish area on an erythematous base was misinterpreted as pseudomembranous colitis.