The goal of this study was to determine if neuropsychological function is associated with adherence to prescribed medication. Altogether, 79 patients with type II diabetes at a VA primary care clinic had adherence to the antihyperglycemic drug metformin measured with MEMS caps over a 4-week period. They completed several tests of neuropsychological function: Mini-Mental Status Exam (MMSE), Trails A and B, Stroop, Digit Span, Digit Symbol, and Grooved Pegboard. In separate multivariate analyses, Stroop word score and time to complete Trails B were independently associated with adherence, as was age. Secondary analyses of the relationship between neuropsychological variables and other adherence-related measures were conducted. Low scores on the MMSE and non-Caucasian ethnicity were associated with missed appointments. None of the neuropsychological variables were associated with glycosylated hemoglobin. These results suggest that cognitive abilities should be considered when counseling patients concerning their adherence.