Background. Family studies of endometriosis indicate that close relatives of patients with endometriosis have an increased risk for the disease, suggesting that genetic components perhaps contribute to endometriosis. The role of allelic variants of the human NAT2 gene needs to be evaluated. Objectives. To determine whether a gene allelic variant of NAT2 is associated with peritoneal endometriosis. Method. Nighty female patients with peritoneal endometriosis diagnosed by laparoscopy were recruited into this study. Results. We have identified a mutation in an allelic variants of NAT2 gene in 75.6% of patients with infertility and peritoneal endometriosis, which exceeds the average rate in the population. In the group of patients who did not achieve pregnancy the presence of heterozygous variants of c.341T>C, c.481C>T, c.590G>A and c.803A>G were 73.2, 73.2, 5.4 and 62.5% respectively. Comparison of allelic polymorphism at different stages of endometriosis showed no significant differences, however, the presence of tree or more "mutant" homozygous allelic variations were significantly higher for stage 3-4 endometriosis patients. Conclusion. NAT2 gene polymorphism could be used as an additional criteria for predicting the effectiveness of infertility treatment in women with peritoneal endometriosis.