OBJECTIVE: To analyse ovarian Sertoli-Leydig cell tumours (SLCTs) for potential prognostic markers and their use for treatment stratification. PATIENTS: Forty-four patients were included. Patients were prospectively reported to the German MAKEI (Maligne Keimzelltumoren) studies (n=23), French TGM protocols (n=10), Italian Rare Tumour Project (TREP) registry (n=6), and the Polish Pediatric Rare Tumour Study group (n=5). Tumours were classified according to World Health Organisation (WHO) and staged according to International Federation of Gynecological Oncology (FIGO). RESULTS: Median age was 13.9 (0.5-17.4) years. All patients underwent resection by tumour enucleation (n=8), ovariectomy (n=17), adenectomy isolated (n=18) or with hysterectomy (n=1). FIGO-stage: Ia 24pts., Ic 17pts., II/III 3pts. One patient had bilateral tumours. Four patients (stage Ia: 3, stage Ic: 1) developed a metachronous contralateral tumour. Otherwise, all stage Ia patients remained in complete remission. Among 20 patients with incomplete resection or tumour spread (stage Ic-III), eight relapsed, and five patients died. Eleven patients were initially treated with two to sixcycles of cisplatin-based chemotherapy. Of these, seven patients are in continuous remission. Poor histological differentiation was associated with higher relapse rate (5/13) compared to intermediate (3/18) and high differentiation (0/4). Tumours with retiform pattern or heterologous elements showed a high relapse rate, too (5/11). After a median follow-up of 62months, event-free survival is 0.70±0.07, relapse-free survival 0.81±0.06 and overall survival 0.87±0.05. CONCLUSIONS: Prognosis of SLCTs is determined by stage and histopathologic differentiation. Complete resection with careful avoidance of spillage is a prerequisite of cure. The impact of chemotherapy in incompletely resected and advanced stage tumours remains to be evaluated.