Familial hypocalciuric hypercalcemia (FHH) is a lifelong, benign autosomal dominant disease characterized by hypercalcemia, normal to increased parathyroid hormone level, and a relatively low renal calcium excretion. Inactivation of the calcium-sensing receptor in heterozygous patients results in FHH, while in homozygous patients as well as in compound heterozygous or dominant negative heterozygous patients, it may result in neonatal severe hyperparathyroidism (NSHPT). Parathyroid surgery is not indicated in FHH and does not lower plasma calcium unless total parathyroidectomy is performed, in which case hypocalcemia ensues. There is currently no definitive medical treatment available, although pamidronate can be used to stabilize these patients before parathyroidectomy. Some NSHPT patients are asymptomatic subsequently in their lives. In this paper, clinical characteristics of this relatively rare disorder are presented.