Swyer syndrome or pure gonadal dysgenesis 46, XY is a medical condition associated with 46 XY karyotype and primary amenorrhea in a phenotypic female. In this syndrome, there is an abnormality in testicular differentiation. Patients with disorders in sexual differentiation have an increased risk for development of genital malignancies. A 14-year-old female admitted with abdominal pain was diagnosed to have Swyer syndrome and a pelvic tumor after clinical and laboratory investigations. She underwent surgery, and the histology report revealed a mixed germ cell tumor in a dysgenetic gonad. She recurred three months later and was successfully treated with chemotherapy and a second surgery to remove the differentiated teratoma. The early diagnosis of patients with Swyer syndrome is important because of the increased risk for the development of malignancy. Early surgical treatment is required. Recurrent and metastatic disease respond well to chemotherapy.