Endometriosis is defined as the presence of ectopic endometrial glands and stroma outside of the uterine cavity. Recent studies have shown that the oxidative stress causes irreparable damage, which leads to oxidative enzymopathies. Catalase gene encodes an antioxidant enzyme, detoxifying hydrogen peroxide to H2O and O2. The aim of this study was to determine whether the polymorphism at position -262 in the promoter region of catalase gene (C-262T), which alters the expression and enzyme blood levels, could have an impact on the risk of endometriosis. Extracted DNA from peripheral blood leucocytes was genotyped using allele-specific PCR (AS-PCR). The χ2-test was used for statistical analyses. In endometriosis subjects, the frequencies of the CAT CC/CT/TT were 67.5%, 32.5% and 0%, respectively, while in healthy women, they were 12%, 68% and 20%, respectively. Significant differences in allele and genotype distribution among controls and patients were found (OR, 178.76 95% CI, 10.11–3159.1202; p = 0.0004). This study indicates that catalase C-262T polymorphism is associated with the endometriosis. Randomised multicentre trials with greater sample sizes are still needed to clarify our results.