Persistent Hyperinsulinemic Hypoglycemia of Infancy (PHHI) is a rare disease characterized clinically by persistent hypoglycemia with inappropriately elevated circulating insulin concentrations. Here we report on 7 pedigrees including 21 cases. The pedigrees are derived from 3 distinct ethnic groups, and include a very large Bedouin family, and Arab family, and 5 smaller pedigrees of Jewish families all of Eastern European origin. Data obtained from these families and from other families reported in the literature strongly suggest that PHHI is inherited as an autosomal recessive disorder.