Swyer syndrome is caused by abnormal sex differentiation during the embryonic period, resulting in incomplete intrauterine masculinization and undifferentiated gonads. The current case report describes a patient with Swyer syndrome associated with stage 3 gonadal dysgerminoma who has survived for 23 years. At age 18, this patient sought assistance for primary amenorrhea from the Gynecological Services Department of the University of Brasília Hospital. A physical examination revealed that the patient was at Tanner stage 4 with respect to axillary hair, breasts, and pubic hair; she presented with a eutrophic vagina and a small cervix. She was treated with a combination of estrogens and progestogens to induce cycling. Approximately 4 years later, a complex tumor was found and resected; a histopathological analysis revealed that this tumor was a right adnexal dysgerminoma with peritoneal affection. The patient was also subjected to chemotherapy. Her follow-up has continued to the present time, with no signs of tumor recurrence. In conclusion, this report describes an extremely rare case in which Swyer syndrome was associated with ovarian dysgerminoma; relative to similar patients, the described patient has survived for an unusually prolonged time.