Hypercalcemia due to neonatal severe HPT (NSHPT) secondary to homozygous or heterozygous mutations of CASR, has been treated since 2011 with cinacalcet, in association with biphosphonates, in order to avoid post-surgical hypoparathyroidism (2, 16, 23, 25, 36, 40). Here, CASR is linked to neonatal severe primary hyperparathyroidism.