We report postpartum hypercalcemia in 2 patients with previous thyroid carcinoma who had undergone total thyroidectomy and total parathyroidectomy and required vitamin D and calcium therapy to control hypoparathyroidism. Postpartum, they required less vitamin D and calcium for satisfactory control. While lactating, they maintained normal serum calcium without supplementary vitamin D or calcium. Transient remission of hypoparathyroidism symptoms has been observed during lactation. Some studies have shown that parathyroid-related protein (PTHrP) is produced by breast tissue, having an endocrine-like effect. We discuss the mechanism of postpartum hypercalcemia.