MUC1 is a mucinous glycoprotein which is overexpressed and under or aberrantly glycosylated in many human malignancies. MUC1 is associated with cellular transformation and can confer resistance to genotoxic agents. L-BLP25 is a peptide vaccine strategy that targets the exposed core peptide of MUC1. In preclinical studies, L-BLP25 induced a cellular immune response characterized by T-cell proliferation in response to MUC1 and production of IFN-gamma. Phase I and II trials have established the dose and schedule of the vaccine as well as its excellent safety profile. A randomized phase II trial of maintenance L-BLP25 versus best supportive care in patients with stage IIIB/IV non-small cell lung cancer who experienced clinical benefit from initial therapy has been reported. Updated survival analysis of this trial continues to show a strong survival trend in favor of L-BLP25 (median survival, 30.6 versus 13.3 months) in a subgroup of patients with locoregional stage IIIB disease. These promising results will be tested in a phase III trial of L-BLP25 versus placebo in patients with stage III non-small cell lung cancer after response to primary chemoradiotherapy.