The seventh case in the world literature of primary hyperparathyroidism in a neonate is reported. This is the fifth case in which an autopsy was performed. The clinical and anatomic findings in all seven cases are reviewed and compared. Neonates with primary hyperparathyroidism show diffuse hyperplasia of the parathyroid glands. The bones show disturbed osteogenesis, bone resorption, and widespread fibrosis of the marrow cavities. Bony cysts are not appreciated. Pathologic fractures are common. Marked hypercalciuria or hyperphosphaturia is usually not observed, perhaps because the immature renal tubules fail to respond to the influence of excess parathormone. Aminoaciduria and anemia are commonly observed. The prognosis is grave, and the etiology of this syndrome remains unexplained.