Menorrhagia is a serious complication in young female oncology patients who suffer from severe thrombocytopenia during myelosuppressive treatment. To the authors' knowledge, little is known regarding the incidence of this complication or the effectiveness of possible therapies for its prevention. In this retrospective clinical study, after a thorough gynecologic evaluation, young female oncology patients with regular menstrual cycles undergoing myelosuppressive treatments received either depo-medroxyprogesterone acetate (DMPA), or D-tryptophan-6-luteinizing hormone-releasing hormone depot treatment (gonadotropin-releasing hormone agonist [GnRH-a]), or no treatment before the administration of myelosuppresive chemotherapy. Only patients who later developed severe thrombocytopenia (<25,000 platelets per muL) were included in the study. Daily blood counts, menorrhagia, nonvaginal bleeding episodes, and the need for blood products, gynecologic consultations, and other medical interventions were determined. Of 101 women with cancer who met the inclusion criteria, 42 patients received DMPA, 39 patients received GnRH-a, and 20 patients remained untreated. The mean duration (+/- standard deviation) of severe thrombocytopenia was 24.76 +/- 23.6 days. Four patients were not included because of significant gynecologic pathologies. General bleeding from nongynecologic sites was similar for all groups and was not associated with vaginal bleeding. Severe or moderate menorrhagia was documented in none of the 39 women who received GnRH-a, in 9 patients (21.4%) who received DMPA, and in 9 untreated patients (40%; P = .02). Fewer calls for urgent gynecologic consultations were documented in the GnRH-a group compared with the untreated group (P < .0001). Female patients undergoing myelosupressive therapy are at high risk of developing significant menorrhagia during prolonged, severe thrombocytopenia. Pretreatment gynecologic evaluation can detect significant pelvic pathologies. GnRH-a treatment effectively prevented menorrhagia, whereas DMPA administration was less effective.