We had previously suggested that women with endometriosis have increased oxidative stress in the peritoneal cavity. In order to assess whether antioxidant supplementation would ameliorate endometriosis associated symptoms, we performed a randomized, placebo controlled trial of antioxidant vitamins (Vitamin E and C) in women with pelvic pain and endometriosis. Fifty nine women, ages 19–41 years, with pelvic pain and history of endometriosis and/or infertility were recruited for this study. Patients were randomly assigned to two groups: vitamin E (1200 IU) and vitamin C (1000 mg) combination or placebo, daily for eight weeks before surgery. Pain scales were administered at baseline and bi-weekly. Inflammatory markers were measured in the peritoneal fluid obtained from both groups of patients at the end of therapy. Our results indicated that, after treatment with antioxidants, chronic pain (“everyday pain”) improved in 43% of patients in antioxidant treatment group (p=0.0055) as compared to the placebo group. In the same group, dysmenorrhea (“pain associated with menstruation”) and dyspareunia (“pain with sex”) decreased in 37% and 24% patients, respectively. In the placebo group, dysmenorrhea associated pain decreased in 4 patients and no change was seen in chronic pain or dyspareunia. There was significant decrease in peritoneal fluid inflammatory markers, RANTES (p≤0.002), interleukin-6 (p≤0.056) and monocyte chemotactic protein-1 (p≤0.016) after antioxidant therapy compared to patients not on antioxidants. In conclusion, results of this clinical trial show that administration of antioxidants reduces chronic pelvic pain in women with endometriosis and inflammatory markers in the peritoneal fluid.