An 8-year-old Japanese girl was admitted with an ovarian yolk sac tumor. Regarding birth history, the patient had been delivered by cesarean section at 25 weeks of gestation with a birthweight of 711g. She had required neonatal intensive care including oxygenation, various medications, and tests. After surgery and chemotherapy, there was no recurrence for 2 years, at the time of writing. Yolk sac tumor, which is a malignant germ cell tumor, is rare in children. Although the cause and risk factors are unclear, it has been reported that malignant germ cell tumors in childhood have been associated with pathophysiology at birth. Given that premature infants are more likely to survive due to advances in perinatal care, it is expected that such cases will increase in the near future. We suggest that children born prematurely require careful follow up.