['To evaluate interleukin (IL)-12 and IL-18 levels in the serum and peritoneal fluid of women with and without endometriosis.', 'Cross-sectional survey.', 'University hospital.', 'Interleukin-12 and IL-18 levels were compared in 105 patients submitted to laparoscopy because of symptoms suggestive of endometriosis (pain and/or infertility). The disease was confirmed in 72 patients (study group), while in 33 patients findings were not compatible with endometriosis (control group). INTEVENTION(S): Blood sample and peritoneal fluid were obtained from patients during videolaparoscopy.', 'The levels of IL-12 and IL-18 in peripheral blood and peritoneal fluid were determined and compared with the stage and site of the disease and histologic classification.', 'IL-12 levels measured in peritoneal fluid were higher in patients with endometriosis compared with the control group. A significant increase in IL-12 levels was found when the more advanced stages of the disease were compared with the initial stages. No statistically significant differences were found in IL-18 levels, either in serum or in peritoneal fluid samples.'] Is interleukin-12 but not interleukin-18 associated with severe endometriosis?