17-beta-Hydroxysteroid dehydrogenase type 3 (17 beta HSD-3) converts. 4 androstenedione (A) to testosterone (T) in the testes. This enzyme plays a key role in androgen synthesis and it is essential for normal fetal development of male genitalia. 17 beta HSD-3 deficiency is a rare cause of 46,XY disorders of sexual development. Here, we report a 16-year-old 46, XY patient with 17 beta HSD-3 deficiency raised as a female and significantly virilized in puberty. A homozygous 7 base pair deletion on exon 10 was determined in HSD17B3 gene (c.777-783del_GATAACC). Our patient had one of the very rare mutations, which was previously unencountered in Turkish patients with 17 beta HSD type 3, and she is the second reported case with this deletion.