Endometriosis is regarded as a complex trait, in which genetic and environmental factors contribute to the disease phenotype. We investigated whether the interleukin (IL) 1beta (+3953) polymorphism is associated with the severity of endometriosis. Diagnosis of endometriosis was made on the basis of laparoscopic findings. Stage of endometriosis was determined according to the Revised American Fertility Society classification. 118 women were enrolled in the study. 78 women did not have endometriosis, 6 women had stage I, 3 had stage II, 13 had stage III and 18 had stage IV endometriosis. Polymerase Chain Reaction (PCR), Restriction Fragment Length Polymorphism (RFLP), and agarose gel electrophoresis techniques were used to determine the IL 1beta (+3953) genotype. Frequencies of the IL-1beta (+3953) genotypes in the control group were: CC, 0.397; TT, 0.115; CT, 0.487. Frequencies of the IL-1beta (+3953) genotypes in cases were: CC, 0.375; TT, 0.225; CT, 0.400. We found a 2.22 fold increase in TT genotype in the endometriosis group. However, the difference was not statistically significant (P > 0.05). We also observed an increase in the frequency of IL-1beta (+3953) T allele in the endometriosis group. However, the difference was not statistically significant. We also investigated the association between IL-1beta (+3953) polymorphism and the severity of endometriosis. The frequencies of CC+CT genotypes in stage I, III and IV endometriosis patients were 83.3, 84/6 and 72.2%, respectively; and TT genotypes were 16.7, 15.4 and 27.8%, respectively. We observed a statistically insignificant increase in TT genotype in stage IV endometriosis (P > 0.05). We suggest that IL-1beta (+3953) polymorphism is not associated with endometriosis in Turkish women.