We designed the present study in order to evaluate the eventual role of polymorphisms in the genes encoding cytochrome P450c17alpha (CYP17) and the progesterone receptor (PROGINS) as risk factors for endometriosis development. Eligible cases consisted of 121 women with surgically confirmed endometriosis who underwent treatment in a hospital in São Paulo, Brazil during the period from September 2003 to September 2005. The 281 controls were participants with normal gynecological as well as pelvic ultrasound evaluation, who did not have any gynecological conditions during their reproductive lives such as pelvic pain and/or dyspareunia nor infertility history. Genomic DNA was obtained from buccal cells and processed for DNA extraction using the GFX DNA extraction kit (GE Healthcare). The CYP17 (-34T-->C) polymerase chain reaction-restriction fragment length polymorphism assay has been described previously, as has the progesterone receptor polymorphism (PROGINS) detection assay. PROGINS heterozygosis genotype frequencies were shown to be statistically higher in endometriosis cases compared with controls. On the other hand, differences in the CYP17 polymorphism (-34T-->C) frequencies were not even close to significance (p = 0.278) according to our findings.