About 7% of patients with calcium urolithiasis suffer from primary hyperparathyroidism. A systematic search for this diagnosis is therefore mandatory in such patients. Because hypercalcemia is often discrete or intermittent, determinations of calcium levels should be repeated at least thrice. Measurement of ionized calcium levels improves the detection of hypercalcemia. The biological diagnosis is based on the presence of hypercalcemia together with an increased plasma level of 1-84 intact parathormone (PTH). A PTH value still in the normal range but inappropriately elevated in the context of hypercalcemia could be sufficient for the diagnosis of primary hyperparathyroidism.