BACKGROUND: Granulosa cell tumors are known to be hormonally active. They usually produce estrogen and inhibin, and the serum inhibin level is often considered a useful tumor marker during the follow-up of this illness. CASE: We present a case of malignant juvenile granulosa cell tumor associated with hyperprolactinemia. In our patient, the serum prolactin concentration closely reflected the behavior of the disease. CONCLUSION: Our findings are consistent with the assumption that prolactin was a tumor marker in this patient.