To determine the efficacy of GnRH analogue plus add-back therapy compared with GnRH analogue alone and estroprogestin in patients with relapse of endometriosisassociated pain. Randomized, controlled study. University hospital. One hundred thirtythree women with relapse of endometriosis-related pain after previous endometriosis surgery. Fortysix women were treated with GnRH analogue plus add-back therapy, 44 women were given GnRH analogue alone, and 43 women received estroprogestin, for 12 months. Pain evaluation by a visual analogue scale, quality of life in treated patients according to the SF-36 questionnaire, and occurrence of adverse effects, including bone mass density loss, at pretreatment, after 6 months of treatment, at the end of treatment (12 months), and 6 months after discontinuation of treatment. Patients treated either with GnRH analogue alone or GnRH analogue plus addback therapy showed a higher reduction of pelvic pain, dysmenorrhea, and dyspareunia than patients treated with oral contraceptive, whereas patients treated with addback therapy showed a better quality of life, as assessed with the SF-36 questionnaire, and adverse effects rate than the other two groups. Addback therapy allows the treatment of women with relapse of endometriosisassociated pain for a longer period, with reduced bone mineral density loss, good control of pain symptoms, and better patient quality of life compared with GnRH analogue alone or oral contraceptive. To determine the efficacy of GnRH analogue plus add-back therapy compared with GnRH analogue alone and estroprogestin in patients with relapse of endometriosis-associated pain. Randomized, controlled study. University hospital. One hundred thirtythree women with relapse of endometriosis-related pain Fortysix women were treated with GnRH analogue plus add-back therapy, 44 women were given GnRH analogue alone, and 43 women received estroprogestin, for 12 months. Pain evaluation by a visual analogue scale, quality of life in treated patients according to the SF-36 questionnaire, and occurrence of adverse effects, including bone mass density loss, at pretreatment, after 6 months of treatment, at the end of treatment (12 months), and 6 months after discontinuation of treatment. Patients treated either with GnRH analogue alone or GnRH analogue plus addback therapy showed a higher reduction of pelvic pain, dysmenorrhea, and dyspareunia than pat ients treated with oral contraceptive, while patients treated with addback therapy showed a better quality of life, as assessed with the SF-36 questionnaire, and adverse effects rate than the other two groups. Addback therapy allows the treatment of women with relapse of endometriosisassociated pain for a longer period, with reduced bone mineral density loss, good control of pain symptoms, and better patient quality of life compared with GnRH analogue alone or oral contraceptive.