INTRODUCTION: It has been discovered that the immune system can recognize, and in some cases control tumor growth. Enhancing T-cell activation is a potent way to amplify anti-tumor immune responses. Ipilimumab is an antibody that blocks the co-inhibitory receptor of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) that functions to attenuate T-cell responses. The drug has been shown to be an effective agent in the treatment of metastatic melanoma. A variety of toxicities have been described, most commonly enterocolitis, hepatitis and skin rashes. We describe a case of Ipilimumab induced lung toxicity.