Abstract: Objective: To present a case of hypercalcemia associated with thyrotoxicosis in a patient with vitamin D deficiency and review biochemical changes during the course of treatment. Methods: We report a case, describe the changes in serum calcium, phosphorus, parathyroid hormone in Graves' disease and concomitant Vitamin D deficiency. We compare our findings to those reported in literature. Results: Our patient had hypercalcemia secondary to thyrotoxicosis alone, which was confirmed by low parathyroid hormone level and resolution of hypercalcemia with treatment of thyrotoxicosis. The case was complicated by a concomitant vitamin D deficiency. Serum calcium elevation in patients with thyrotoxicosis occurs secondary to hyperthyroidism