Joint cartilage calcification was found in 16 of 91 patients (18 per cent) with primary hyperparathyroidism. The calcification was most common in the knees (menisci and articular cartilage) and in the wrists (triangular cartilage). The roentgen evidence of cartilage calcification in a patient with appropriate symptoms and clinical changes may lend support to the presumptive diagnosis of primary hyperparathyroidism. A possible mechanism of cartilage calcification in primary hyperparathyroidism is discussed.