We report on a brother and sister with hyperinsulinism and nesidioblastosis of the pancreas. In addition, one brother and one sister who died in the neonatal period were probably affected. The parents of these children were healthy and consanguineous. We think that this is strongly suggestive of autosomal recessive inheritance. Seven other reports of presumed autosomal recessive hyperinsulinism are reviewed. To our knowledge, we report the first case in sibs whose parents were consanguineous. We think that early recognition of the condition is of obvious importance not only for therapy, but also for purposes of genetic counseling.