BACKGROUND Very young children with central nervous system malignant brain tumors have a poor prognosis. As compared with older children, survival is less likely, and those children who do survive frequently have severe impairment of growth and cognitive abilities, resulting partly from treatment with radiotherapy. Therefore, an intensive chemotherapeutic regimen was used to treat children younger than 2 years of age with a diagnosis of malignant astrocytomas. METHODS Thirty-nine children younger than 24 months of age who were diagnosed with malignant astrocytoma were treated on a Childrens Cancer Group protocol with an eight-drug chemotherapeutic regimen (vincristine, carmustine, procarbazine, hydroxyurea, cisplatin, cytosine arabinoside, prednisone, and dimethyl-triazenoimidazole-carboxamide) after surgery and postoperative staging. Radiation therapy was to be deferred until the completion of chemotherapy. RESULTS The objective response rate after two cycles of chemotherapy was 24%. Most patients did not receive radiotherapy. Progression-free survival (PFS) and survival at 3 years was 36% (standard error, 8%) and 51% (8%), respectively. The PFS of those children with anaplastic astrocytoma was 44% (11%), significantly better than that of glioblastoma multiforme (GBM) (0%). Extent of resection was not associated significantly with PFS, but tumors within the cerebral hemispheres were associated with a more favorable prognosis. Tumor progression occurred locally in almost all cases and early in treatment (median PFS, 8 months). CONCLUSIONS Chemotherapy appears to be effective primary adjuvant treatment for some very young children with anaplastic astrocytomas. Overall, however, survival remains poor, especially for children with GBM. Strategies to improve outcome require early intervention, because tumor progression occurs soon after diagnosis in the majority of patients.