Ipilimumab (Yervoy®) is an anti-cytotoxic T-lymphocyte antigen (CTLA)-4 monoclonal antibody that has been approved in the US for the first- or second-line treatment of patients with malignant melanoma. In the EU, it is awaiting approval as second-line therapy for melanoma. Ipilimumab blocks the effects of the negative T-cell regulator CTLA-4, which may in turn augment T-cell responses to tumour cells. Preclinical studies have indicated that antibody blocking of CTLA-4 can lead to potent immune responses. Ipilimumab is also in development as first- and second-line therapy for prostate cancer where it has progressed to phase III clinical trials worldwide, and it is in phase II development for non-small cell lung cancer. Ipilimumab was originated by the University of California, Berkeley, in the US and subsequently licensed to Medarex, which was later acquired by Bristol-Myers Squibb. This article summarizes the milestones in the development of intravenous ipilimumab leading to this first approval. This profile has been extracted from Wolters Kluwer's R&D Insight drug pipeline database. R&D Insight tracks drug development worldwide through the entire development process, from discovery, through pre-clinical and clinical studies to market launch.