One hundred patients with brain tumors were diagnosed and treated during the first 24 months of life. They represent 16% of 608 children with brain tumors treated from 1952 through 1984. The most common histological type of brain tumors during the first 24 months are benign astrocytoma, medulloblastoma, and choroid plexus papilloma. The tumor location is distributed relatively evenly among the cerebellum and the 4th ventricle, the cerebral hemisphere (including the lateral ventricle), and the suprasellar region and 3rd ventricle. The chief presenting signs and symptoms are a full fontanelle, macrocephaly, changes of behavior, and delayed developmental milestones. Localizing signs are infrequent. Ninety-two patients underwent craniotomy with a one-month surgical mortality rate of 12%. The surgical mortality rate was 5.6% among 36 recent patients diagnosed by computed tomography. The 5-year survival rate is 41% in the patients younger than 12 months and 74% in patients diagnosed during the 2nd year of life. This study indicates the validity of Collins' rule for medulloblastomas during the first 24 months of life, but not for benign or malignant astrocytomas.