Disorders of sex development (DSD) result from intrauterine defects in sex discrimination. The clinical phenotype differs based on the disease type. Cases with ambiguous external genitalia are diagnosed at birth. However, diagnosis of cases with normal-appearing external genitalia may be delayed until puberty. Here, we report a patient with a pelvic mass and a small uterus that was diagnosed by abdominal ultrasound, in addition to the history of primary amenorrhea and physical examination suggested Swyer syndrome, confirmed by genetic karyotyping. Pathological examination of the surgically removed mass revealed dysgerminoma. Until the age of 19, the patient did not have any idea about 46, XY karyotype, and assumed to be a female. The development of dysgerminoma (as a result of the simultaneous presence of gonadal dysgenesis and Y-chromosome) was another challenge that the patient had to deal with. The diagnosis of this patient at an earlier age could have prevented the development of gonadoblastoma, by removal of the streak gonads. By the presentation of this case, we intend to increase the physician’s awareness about DSDs; earlier diagnosis may help the patient deal with her disease better and reduce the risk of further complications.