In order to assess the effectiveness of GnRH-agonist (GnRH-a) therapy in the treatment of endometriomas, with or without surgical intervention, 26 women with laparoscopically proven endometriomas, greater than 3 cm diameter were recruited to the study.Fourteen women who had 19 endometriomas (5 of them were bilaterally), had drainage of endometrioma at the initial laparoscopy. After the procedure, they had ovarian suppression with GnRH-a therapy for 6 months.The second group which consisted of 12 women, had 17 endometriomas. No surgical procedure was performed. They received only GnRH-A therapy for 6 months. At the second -look laparoscopy, the rates of decrease in ovarian AFS scores of endometriomas and complete resolution were found as 100% and 36.8% respectively, in the first group, In the second group the response was only 17.6% (p<0.0001).In this prospective study we found that drainage of the cyst (surgical therapy) combined with the postoperative GnRH-a suppression is a better treatment modality for endometriomas. Than the use of GnRH-a (medical therapy) alone.