Recent advances in the genetics of the family of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) enzymes have helped in the understanding of the molecular basis and hormonal phenotype of bona fide 3 beta-HSD deficiency congenital adrenal hyperplasia (CAH). This article revisits the clinical spectra of 3 beta-HSD deficiency disorders, pathophysiology of 3 beta-HSD deficiency CAH, and updates genotype findings and diagnostic hormonal criteria for bona fide classic and nonclassic 3 beta-HSD deficiency CAH. The delta-5 steroid abnormality for the nonclassic 3 beta-HSD deficiency CAH, proven by genotype study, is substantially greater than the hormonal criteria for the disorder published before the advent of molecular information on the gene encoding adrenals and gonads in humans. In hyperandrogenic children and women, the pathogenic mechanism of a subtle abnormality in adrenal 3 beta-HSD activity, determined by modestly elevated ACTH stimulated delta-5 steroid levels, which led to the diagnosis of mild nonclassic 3 beta-HSD deficiency in the past, is outside of the type II 3 beta-HSD gene which encodes adrenals and gonads in humans and remains to be further explored.