Our aim was to determine the effect of metformin exposure on survival in patients with advanced pancreatic adenocarcinoma (PAC). A retrospective cohort study was conducted using The Health Improvement Network, a primary care electronic medical record database from the United Kingdom (2003-2010). The study cohort included all subjects with a diagnostic code for incident PAC and a preexisting diagnosis of type 2 diabetes mellitus. Subjects were classified as exposed if they were prescribed metformin around the time of PAC diagnosis (between 6 months prior and 1 month after). A secondary analysis was performed only on exposed subjects without prior (ie, 6 months before PAC diagnosis) exposure to metformin. The primary outcome was overall survival. The analysis was performed using univariate and multivariable Cox proportional hazards models. The study included 516 subjects with preexisting type 2 diabetes mellitus and PAC, 247 of which were exposed to metformin. In univariate and multivariable analysis, there was no difference in survival between those exposed and those unexposed to metformin in the primary analysis (hazards ratio, 1.11 0.89-1.38, P = 0.367) or the secondary analysis (hazards ratio, 1.09 0.80-1.47, P = 0.585). Metformin use is not associated with improved survival in subjects with advanced PAC.