A substantial threat to the overall health of the American public is nonadherence to medications used to treat diabetes, as well as physicians' failure to initiate patients' use of those medications. To address this problem, we evaluated an integrated, pharmacy-based program to improve patients' adherence and physicians' initiation rates. The study included 5,123 patients with diabetes in the intervention group and 24,124 matched patients with diabetes in the control group. The intervention consisted of outreach from both mail-order and retail pharmacists who had specific information from the pharmacy benefit management company on patients' adherence to medications and use of concomitant therapies. The interventions improved patients' medication adherence rates by 2.1 percent and increased physicians' initiation rates by 38 percent, compared to the control group. The benefits were greater in patients who received counseling in the retail setting than in those who received phone calls from pharmacists based in mail-order pharmacies. This suggests that the in-person interaction between the retail pharmacist and patient contributed to improved behavior. The interventions were cost-effective, with a return on investment of approximately $3 for every $1 spent. These findings highlight the central role that pharmacists can play in promoting the appropriate initiation of and adherence to therapy for chronic diseases.