ABSTRACT The obstetric and metabolic observations made in a woman suffering from hyperparathyroidism and her newborn infant are described. The significant findings were: 1) slight maternal hypercalcaemia, 2) a high calcium concentration in amniotic fluid, 3) a foetal hypercalcaemia greater than that in the mother, 4) a low serum calcium concentration during the first few weeks of life but no manifest tetany, 5) a higher than normal plasma alkaline phosphatase level in the newborn but no bone disease demonstrable by X-ray, and 6) a lower content of calcium in the mother's milk than in normal human milk. Pregnancy, labour and delivery were uneventful. A study of the literature comprising 23 females with a minimum of 34 pregnancies during their disease, shows that these females suffered from a more severe disease than 138 patients in a consecutive series of cases of hyperparathyroidism during about the same period (1930–1960). Since the relative number of patients with bone disease has decreased during the last 10–15 years we believe that the risks for perinatal death and tetany observed in this review, i. e. about 25 and 50 per cent, respectively, are greater than would be expected in a consecutive series today. A severe reduction in fertility is presumably not present. Labour and delivery are not interfered with, but there seems to be a tendency toward a low birth weight. Indirect evidence for renal damage and hypertension as the cause of stillbirth and neonatal death is given. Since no case of infantile osteitis fibrosa was observed it is concluded that the maternal parathyroid hormone does not pass freely through the placental barrier. The treatment is discussed.