Imperforate hymen is a rare congenital abnormality. It often presents with abdominal mass associated with pain. Differential diagnosis includes abdominal malignancies. A thirteen years-old female was referred to our center with abdominal distention and pain with the presumptive diagnosis of abdominal malignancy. Serum levels of tumor markers were extremely high. Abdominal CT scan without contrast revealed an extremely large, cystic mass (hematocolpos) with thickened walls. Gynecologic examination revealed imperforated hymen. A midline vertical hymenal incision was performed. This case is unique in terms of high suspicion of malignancy in light of physical examination, CT scan characteristics and high levels of tumor markers. It emphasizes that gynecologic examination should be a part of routine physical examination in adolescent females presenting with abdominal mass.