Primary hyperparathyroidism during pregnancy lias been reported in 36 women; 1 new case is reported here. Screening by determining serum calcium levels is a valuable method of diagnosing the disease. Kad minium noassay of serum parathyroid hormone (PTH) greatly aids in the diagnosis. Amniotic fluid PTH values are discussed. Hyperparathyroidism has a high association with progressive renal insufficiency, renal calculi, hypertension, and bone disease. During pregnancy, there is an increased incidence of stillborns, premature labor, and neonatal tetany. Acute hyperparathyroid crisis may result in maternal death. This is the first reported case surgically treated during the third trimester of pregnancy. Surgery should be considered when the diagnosis is made late in pregnancy, as this may protect the infant from neonatal tetany.