Administration of cyclophosphamide (CYC), an alkylating agent used to treat malignancies and severe rheumatic diseases, creates a risk of ovarian insufficiency that is related to the intensity and duration of therapy and the age of the patient. To preserve reproductive capacity in the appropriate clinical setting, oocyte, embryo, and/or ovarian tissue cryopreservation are recommended. Medical protection with depot gonadotropin-releasing hormone agonists (GNRHa) has emerged as a potential means to preserve both fertility and ovarian function through the suppression of ovarian activity during treatment with alkylators. We review the trials of GNRHa for ovarian protection in both cancer and rheumatic disease patients. Trials in cancer patients receiving CYC alone, or in combination with other gonadotoxic agents that have employed several different GNRHa have yielded mixed results. Trials in lupus patients receiving lower doses of CYC alone utilizing depot leuprolide acetate have tended to show favorable results.