We reported a case of a 41-year-old woman who had been diagnosed with Gitelman's syndrome since the age of 31 years. The diagnosis was established by the typical biochemical pictures including renal wasting hypokalemia, hypomagnesemia, hypocalciuria, metabolic alkalosis, and hyperreninemic hyperaldosteronism. She had normal blood pressure and had never used diuretics. She had a sibling with similar syndrome. The patient was treated with oral potassium and magnesium supplementation. She began to have hypercalcemia at the age of 39 years. The diagnostic approach to hypercalcemia became more complicated because of normal parathyroid hormone levels and underlying hypocalciuria due to Gitelman's syndrome. Thorough evaluation eventually identified primary hyperparathyroidism as the cause of hypercalcemia. To our best knowledge, this is the first report of combined occurrence of Gitelman's syndrome and primary hyperparathyroidism in the literature.