Synovial sarcoma is an aggressive soft tissue sarcoma, which most often occurs in the limbs near the joints. It accounts for 5-10% of all soft tissue sarcomas. It extremely rarely affects the pelvis. So far, only 4 cases of primary involvement of the adnexa have been described. We present a case of a 77-year-old female patient diagnosed with a rapidly growing pelvic formation, subsequently diagnosed as monophasic synovial sarcoma of the ovary. Synovial sarcoma derived from the adnexa is a rare disease that is virtually unknown. The diagnosis is complex, and there is a poor prognosis.