To compare patients with advanced stage endometriosis with control patients without endometriosis with respect to serum Copper (Cu) and Ceruloplasmin (Cp) levels and oxidative stress markers in order to evaluate the importance of these parameters in the pathogenesis of endometriosis. A total of 72 women who underwent laparoscopy or laparotomy for evaluation of infertility, pelvic pain, pelvic mass, tubal ligation or endometriosis were enrolled for this prospective clinical study. Patients were divided into two groups by visual diagnosis at surgery and histological confirmation of endometriosis: control patients (n=41) without endometriosis and study group (n=31) with stage III/IV (advanced stage) endometriosis. Serum Cu, Cp, total antioxidant status (TAS), total oxidant status (TOS), oxidative stress index (OSI), paraoxonase-1 (PON-1), malondialdehyde (MDA), triglyceride (TG), total cholesterol (TC), high-density lipoprotein (HDL) and low-density lipoprotein (LDL) levels were compared between the two groups. Correlations between Cu, Cp and oxidative stress markers were determined. Serum TOS, OSI, Cu, Cp, TG, TC, LDL were significantly higher, whereas TAS, PON-1 activity and HDL were significantly lower, in women with advanced-stage endometriosis than in control groups. There was no difference in serum MDA activities between the two groups. Positive correlations were found between Cu and TOS, Cu and OSI, Cu and Cp, while a negative correlation was found between Cu and PON-1 in the advanced-stage endometriosis group. Positive correlations were found between Cp and TOS, and Cp and OSI in the advanced-stage endometriosis group. Cu and Cp appear to be associated with the etiopathogenesis of and oxidative stress in endometriosis.