Some of the anatomic endocrine, and genetic aspects of lipoid adrenal hyperplasia were studied in an inbred Israeli-Arab family with two affected sibs. One sib, a genetic female, presented with acute Addisonian crisis. Endocrine studies documented elevated ACTH levels and no detectable steroids of gonadal or adrenal origin. The other patient, a male pseudo-hermaphrodite, was found at autopsy to have typical lipoid adrenal hyperplasia and ectopic adrenal tissue adjacent to an intra-abdominal testicle. Complete vagina, uterus, and fallopian tubes were present in addition to the Wolffian structures. This unique observation supports the view that steroids may be necessary for Müllerian inhibitory factor to induce regression of Müllerian structures. The segregation of 27 autosomal markers was studied in one affected and five unaffected sibs. Genetic linkage to HLA, MNS, and GPT is unlikely. In addition, the affected sib is heterozygote for a haplotype of chromosome 1 which includes the Rh, Fy, PGM-1 systems. Determination of fetal gender by the combined use of ultrasonography and amniocentesis is suggested for prenatal diagnosis and improved risk counselling.