An 18-year-old, G0, with primary amenorrhea consulting because of a rapidly enlarging abdominal mass was diagnosed with Swyer syndrome or 46 XY pure gonadal dysgenesis and subsequently underwent staging laparotomy for mixed germ cell tumor (dysgerminoma and yolk sac tumor) arising from her dysgenetic gonad. Bleomycin, etoposide, cisplatin regimen for three to four cycles was planned but the patient was lost to follow-up. A prompt evaluation of her amenorrhea and a timely gonadectomy could have averted the development of malignancy.