Anti-cytotoxic-T-lymphocyte associated antigen-4 (anti-CTLA4), and anti-programmed cell death 1 (anti-PD1) immunotherapies are considered first-line treatments for advanced melanoma. However, the use of these agents is limited by gastrointestinal toxicity such as diarrhea and colitis. The risk of developing these adverse events is poorly defined. As such, our aim was to determine the incidence and relative risk of diarrhea and colitis due to each class of immunotherapy in patients with advanced melanoma.