Anti-cytotoxic T-lymphocyte antigen-4 monoclonal antibody therapy is a new class of drug which has demonstrated increased overall survival in patients with metastatic melanoma. Anti-CTLA-4 antibody therapy inhibits the CTLA-4 inhibitory signal, thereby enhancing the anti-tumor response of the cytotoxic T lymphocytes. This response can lead to a variety of immune-related adverse events. Many of these events are present on follow-up PET/CT examinations performed to assess response to therapy. It is important for the interpreting physician to be aware of the findings on PET/CT to avoid diagnosing adverse events as progressive disease and to alert clinicians regarding these complications.