Background & objectives: Endometriosis is one of the most commonly encountered benign problems in gynaecology. It is frequently associated with chronic pelvic pain, dysmenorrhoea, menorrhagia and dyspareunia, which lead to infertility. To determine the possible association between polychlorinated biphenyls (PCBs) and GSTM1 null (*0/*0) mutation and their possible impact in the pathogenesis of endometriosis. Methods: Ninety seven women with endometriosis mean age (28.5 [+ or -] 6.5 yr) diagnosed by laparoscopy and 102 women without endometriosis (28.4 [+ or -] 4.8 yr) were included. Heparinised blood samples were collected from all for DNA isolation and estimation of PCBs. GSTM1 genotyping was done by PCR and PCBs were estimated by gas chromatography.