<p>Ovarian germ cell tumors (OGCTs) arise from primordial germ cells and are the second most common ovarian neoplasms after surface epithelial tumors. While the majority are benign, approximately 5% are malignant, with mixed germ cell tumors (MGCTs) representing a rare subtype. Accurate diagnosis can be challenging due to overlapping clinical and pathological features, necessitating immunohistochemistry (IHC) for confirmation. We report a case of a 26-year-old unmarried girl presenting with progressive abdominal distension. Imaging revealed a large left adnexal mass with gross ascites. Tumor markers showed elevated LDH levels. Cytology and imaging favored a germ cell tumor. The patient underwent a diagnostic laparoscopy with ascitic fluid drainage and left adnexal mass excision with multiple omental biopsies. Histopathological examination initially suggested a mixed germ cell tumor, stage IIIB, with a predominant yolk sac tumor component. However, immunohistochemistry played a crucial role in confirming the diagnosis, i.e., a predominant dysgerminoma component with a more favorable prognosis. The patient is currently undergoing adjuvant chemotherapy with the BEP regimen (Bleomycin, Etoposide, and Cisplatin). This case underscores the critical role of immunohistochemistry in diagnosing mixed OGCTs, especially when tumor markers and histology are discordant. A multidisciplinary approach, fertility-sparing surgery, and adjuvant chemotherapy form the cornerstone of effective treatment. Early detection and accurate subtyping are vital for prognosis and tailored therapy in young patients.</p>