PURPOSE To describe prescriber response to unsolicited patient reports from the Massachusetts prescription drug monitoring program (PDMP). METHODS Prescribers were surveyed upon receipt of unsolicited reports of their patients' prescription history and three months later. We assessed prescribers' awareness of other prescribers listed in the report, their clinical assessment of medical necessity of all prescribed medications, actions taken by prescribers after receiving the report, and usefulness of the report. RESULTS Of the 333 respondents to the initial survey, only 28 (8.4%) were aware of most, all, or nearly all other prescribers. A total of 146 (43.8%) reported having sufficient knowledge to determine whether the prescriptions were medically necessary, of whom 102 (69.6%) felt the prescriptions were unwarranted. Of the 163 respondents to the follow-up survey, 31.3% added the report to the patient's file, 22.7% discussed the report with other prescribers on the report, 21.5% took no action, and 6% discussed the report with the patient (representing two-thirds of respondents who saw the patient after receiving the report). Most respondents felt that the report was useful for their practice and easy to understand. CONCLUSIONS Unsolicited reporting of PDMP data has the potential to improve clinical practice by alerting providers about patients with multiple prescribers and potentially medically unnecessary prescriptions.