A 13-day-old female infant was admitted with hydrocephalus that had been diagnosed on prenatal ultrasound at 33 weeks' gestation. She was delivered by Caesarean section at 34 weeks with an Apgar score of 10. On admission, she weighed 2,103 g. The head circumference was 32.3 cm, and the fontanelle was tense. T-1- and T-2-weighted MR images revealed an isointense mass occupying the fourth ventricle with multiple cysts in the vermis. The mass was not enhanced after gadolinium administration. CT showed no definite calcification in the lesion. Preoperatively, vermian tumors, including medulloblastoma, ependymoma, astrocytoma, and hamartomas, were considered in the differential diagnosis. Hamartoma was strongly suspected due to the lack of enhancement on MRI. After a suboccipital midline craniotomy, subtotal resection of a soft grayish tumor with areas of hematoma was carried out. The pathological diagnosis was medulloblastoma. Despite chemotherapy, CSF dissemination resulted in death at 11 months. We report this case of congenital medulloblastoma with atypical MRI findings and discuss the clinical characteristics of this lesion. Copyright (c) 2008 S. Karger AG, Basel.