Patients who had an acute myocardial infarction or other atherosclerotic event and had filled a prescription for an HMG-CoA reductase inhibitor were identified for analysis. Compliance was assessed using a multiple-interval refill compliance score. The mean compliance score was 80% and six refill patterns were identified. Regression analysis revealed three factors associated with compliance: (1) days' supply, (2) number of total concomitant medications, and (3) cost sharing. Strategies for improving compliance that may have merit include providing patients with 60- or 90-day supplies (rather than 30-day supplies), controlling the number of other medications prescribed, and lowering copayments for these important medications.