17-beta-Hydroxysteroid dehydrogenase type 3 deficiency is a rare autosomal recessive cause of 46, XY disorder of sex development. Worldwide, about 30 mutations in the hydroxysteroid (17-beta) dehydrogenase 3 (HSD17B3) gene have been reported, involving all exons except exon 1. Herein, we investigated an Egyptian female with 46, XY karyotype and low testosterone/Delta 4-androstenedione ratio. Genomic DNA was extracted from blood samples, and then, direct DNA sequencing of HSD17B3 gene was performed. The patient had a homozygous mutation c. 198G>A in exon 1 resulting in a stop codon (p.W50X). The study presents the first mutation to be reported in exon 1 of the HSD17B3 gene. Copyright (C) 2013 S. Karger AG, Basel