Vitamin D deficiency is a pandemic problem mostly diagnosed in elderly. Few studies are available exclusively done on the topic among young adults. Specific professions such as medical students may have higher risk for developing hypovitaminosis D. We aimed to assess the vitamin D status in medical students of Iran University of Medical Sciences; and to define a cut-off point for 25-hydroxyvitamin-D (25(OH)D) level based on secondary hyperparathyroidism.This was a cross-sectional study on 100 medical students conducted during October 2012. Serum 25(OH)D, intact parathyroid hormone (iPTH), and calcium were measured. Age, sex, body mass index, daily dietary fish and egg consumption, sun exposure, and sunscreen usage were recorded. The association between serum 25(OH)D and iPTH was assessed. Receiver operating characteristics curve analysis was performed.25-hydroxyvitamin-D level was <30 ng/ml in 99% of all participants, and <20 ng/ml in 77%. Mean serum 25(OH)D level was 16.8 ± 4.7 ng/ml. iPTH level in the group with 25(OH)D level of <10 ng/ml was significantly higher than in those with serum 25(OH)D level of 10 to <20 ng/ml and 20 to <30 ng/ml (109 ± 47 pg/ml, 47 ± 27 pg/ml and 46 ± 19 pg/ml, respectively; P = 0.0001). There was a significant linear inverse correlation between serum iPTH and 25(OH)D (r = -0.36, P = 0.0001). 25(OH)D level of 15.4 ng/ml was determined as the optimal cut-off point in detecting possible secondary hyperparathyroidism.To improve the community vitamin D status, in addition to population-based food fortification programs, educational programs seem essential; not only for general population, but also for the more educated groups.