Objective-The aim of this study was to determine whether or not continuous combined HRT used with GnRH-a for the treatment of endometriosis can prevent hypoestrogenic side effects associated with GnRH-a. Methods-Forty premenopausal women with laparoscopically proven endometriosis entered the study. The patients were randomized into two groups. Group I (n = 19)! received 3.75 mg IM leuprolide acetate (LA) ever); 4 weeks for 24 weeks. Group II (n = 21) received 3.7 mg LA combined with 1.25 mg oral conjugated equine estrogen (CEE) and 5 mg oral medroxyprogesterone acetate (MA). Results-Total revised AFS score as well as total pelvic pain scores decreased significantly (P <.001) in both groups. However, a statistically significant difference of hot flushes and sweating was reported by women receiving LA + HRT as compared to those treated with LA alone (P <.001). Furthermore, the bone loss at the lumbar spine was 4.2% in group I compared to 0.9% in group II at the end of the study.;. Conclusions-This study suggests that 1.25 mg CEE + 5 mg MA is effective in preventing hypoestrogenic side effects caused by GnRH-a, while the treatment of endometriosis is not impaired.