Maternal primary hyperparathyroidism causing hypercalcemia during pregnancy can suppress fetal and neonatal parathyroid hormone secretion. We report a newborn with transient hypoparathyroidism presented by hypocalcemic seizure and tetany on the 21st postnatal day in whom the final diagnosis was asymptomatic maternal primary hyperparathyroidism. Neonatal hypocalcemia usually occurs early in life in infants of maternal primary hyperparathyroidism, and although it is very rare, further investigation for unexplained late-onset hypocalcemia may reveal this diagnosis.