Mycophenolate Mofetil (MMF) is a frequently used medication for the maintenance of immunosuppression in pediatric renal transplant patients. It is known to cause mild gastrointestinal side effects. Severe colitis due to MMF is rare and is only described in adults. We report 2 children who presented with severe colitis due to MMF. Infectious and other causes of diarrhea were ruled out. Our patients had diverse histologic findings on colonic biopsies. Patient 1 had histologic features similar to inflammatory bowel disease and patient 2 to graft versus host disease. Withdrawal of MMF resulted in the complete resolution of symptoms in both patients suggesting a causal association. These cases underscore the importance of considering MMF-induced colitis in any patient who presents with diarrhea while on MMF therapy.