Objective: To evaluate safety and efficacy of Mifepristone (RU 486) in medical treatment of endometriosis after recurrence of symptoms following conservative surgery. Patients and Methods: 23 women with severe endometriosis (Stage IV. score >40: Revised AFS classification) were enrolled. All had recurrence of symptoms after conservative surgery. Associated adenomyosis and patients receiving other treatments within 3-months were excluded. Mifepristone was given as 50 mg/day orally continuously for 6 months. Patients were followed up at 1. 3 and 6 months. Ultrasound was performed at baseline and end of therapy.