Male pseudohermaphroditism caused by steroid 5 alpha-reductase deficiency is an autosomal recessive disorder. The enzyme steroid 5 alpha-reductase 2 (encoded by the SRD5A2 gene) catalyses the conversion of testosterone to dihydrotestosterone, which is required for normal differentiation of the external male genitalia, This report describes the molecular analysis of the 5 alpha-reductase type 2 gene in a Bazilian patient who was raised as a female, underwent a reversal of gender role behavior, and is now a married man. This patient is a compound heterozygote bearing an A-->G mutation within exon 2, changing codon 126 from Glu to Arg on one allele and a novel single base deletion (418delT) causing a frameshift mutation at codon 140 in the same exon, on the other allele. This last mutation probably leads to the synthesis of a truncated protein, because a premature termination signal is created at codon 159. Am. J, Med. Genet, 87:221-225, 1999, (C) 1999 Wiley-Liss,Inc.873221225