Long-term use of lithium is a known risk factor for hypercalcemia often due to involvement of the parathyroid gland. Because of this, lithium-induced hypercalcemia typically occurs simultaneously with abnormal parathyroid hormone concentrations. This case report describes a 54-year-old white male who has received lithium therapy intermittently for more than 10 years. During admission to an acute inpatient psychiatric unit, the patient experienced hypercalcemia with normal parathyroid hormone concentrations and no other discernible cause. Based on the Naranjo algorithm, lithium was determined to be the probable cause of hypercalcemia. Current literature suggests that lithium-induced hypercalcemia occurs secondary to hyperparathyroidism; however, this case may provide evidence of another, unidentified cause.