It is well known that Down's syndrome is sometimes associated with leukemia. However, there have been only a few case reports of a relationship between Down's syndrome and brain tumors. We report 2 cases with histological diagnoses of germinoma. The 1st case was a 10-year-old boy with Down's syndrome complaining of seizure and left hemiparesis. Computed tomographic (CT) scan and magnetic resonance imaging (MRI) showed a mass lesion in the right basal ganglia and thalamus. Histological examination indicated two cell pattern germinomas. The 2nd case was a 20-year-old man with Down's syndrome complaining of headache and vomiting. CT scan and MRI showed a pineal region tumor with marked hydrocephalus. Surgical specimens showed typical germinoma. Only 13 cases of brain tumors associated with Down's syndrome have been reported. A higher incidence of germ cell tumors seems to be related to chromosomal abnormalities.