Over the last 40 years, cryptosporidium has increasingly been recognized as a cause of acute self-limiting diarrhea in normal hosts. In the immunocompromised patient, cryptosporidium may cause severe illness with prolonged diarrhea and malabsorption. Pharmacologic therapy of cryptosporidium relies on adequate delivery of drug metabolites to the colon. Here we describe a patient who developed toxic megacolon during induction therapy for leukemia, requiring ileostomy formation to proceed with leukemia...