RATIONALE, AIMS AND OBJECTIVE: Changes in physician behavior are difficult to accomplish. We hypothesized measuring physicians’ vitamin D levels would increase measurement of their patients’ levels. METHODS: We recruited faculty via e-mail. We measured physicians’ serum 25(OH)D levels and asked them to complete a questionnaire created to assess the risk of vitamin D deficiency. Physicians received their vitamin D test results by mail. We monitored physicians’ vitamin D testing rate per 100 patient visits in the 12 weeks before and after receipt of their own vitamin D test result. RESULTS: Twenty-eight (22%) of 126 primary care physicians participated in the study; all were Caucasian and 17 (61%) were women. Gender, practic type, and year of graduation from medical school were similar in participants and non-participants. Over half of participants took a multivitamin and a third took a vitamin D supplement. Although 6 (21%) reported a recent fracture, only 1 physician carried a diagnosis of osteopenia or osteoporosis. At baseline, geriatricians ordered 14 vitamin D tests per 100 patient visits, while internists and family practitioners ordered substantially fewer tests (2 and <1 tests per 100 visits, respectively). After study participation, vitamin D testing rates increased significantly among family practitioners (rate ratio 3.27, 95% CI 1.29-8.33) and internists (rate ratio 3.19, 95% CI 1.12-9.07). Physicians with heavier clinic workloads were half as likely (rate ratio 0.50, 95% CI 0.32-0.76) as those with lighter clinic workloads to increase vitamin D testing rates. Surprisingly, physicians with hypovitaminosis D demonstrated no change in vitamin D testing rates. CONCLUSIONS: Physicians with low vitamin D testing rates were receptive to a personal intervention involving measurement of their own vitamin D levels. High workload appeared to attenuate this effect. These novel but preliminary observations require confirmation in future studies.