Endometriosis seems to be the result of a complex interaction between environmental factors and various genes. In this regard, the cytochrome subfamily 17 (CYP17) may play an important rote by altering the biosynthesis of sex steroids. CYP2C19 is also an important member of the cytochrome P450 (CYP) family, and related mutations may result in an inability to fully metabolize environmental chemicals and cytokines, Leading to several diseases. This study sought to determine whether there is a relationship between endometriosis and CYP17 T>C, CYP2C19*2 and CYP2C19*3 polymorphisms. When samples from 46 patients with endometriosis and 39 healthy controls were analysed, A2A2 type mutation of the CYP17 gene was observed to be more frequent in patients with endometriosis (34.8 versus 7.7%, P=0.003). No association was found between the severity of endometriosis and CYP2C19*2 or CYP2C19*3 polymorphisms of the CYP2C19 gene. These results suggest that mutations related with sex steroid metabolism seem to have an important role in endometriosis. However, the relation between detoxification ability and endometriosis should be examined in further studies with larger sample sizes. (C) 2009, Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.