Diarrhea is one of the most common complaints in oncologic patients. Causes are multiple including bowel resection, infections, radiation and systemic anti-cancer treatments. In the latter case, the pathophysiology is partially elucidated and requires the etiology to be precisely identified : chemotherapy, targeted therapy or immunotherapy. Loperamide remains central in uncomplicated cases. However, with development of immunotherapy, autoimmune mechanism should be recognized and requires different approach based mainly on corticosteroids. Physician taking care of patients with diarrhea should therefore identify possible causes in order to offer adapted treatments and therefore reduce morbidity and mortality.