The history of a pregnant woman with primary hyperparathyroidism is presented. The patient underwent successful operation during the second trimester and the subsequent pregnancy and delivery were completely normal. Previously, 72 women with an established diagnosis of hyperparathyroidism in pregnancy are reported in the English literature. Twenty-three women underwent operation during pregnancy and 18 normal children were born. Fifty women with a total of 79 pregnancies during a hyperparathyroid state bore 35 normal children while 40 births had different kinds of complications. It is thus clearly documented that the risk of severe fetal complications is much higher if the hyperparathyroidism is left untreated than if the mother undergoes operation during the pregnancy. Therefore when the diagnosis is established the mother should undergo operation, if possible during the second trimester, which minimizes the complication rate significantly in both mother and child. Correction of the hypercalcemic state enables the development of adequate parathyroid gland function in the baby.