The authors conducted a study of 21 children with benign astrocytomas in the IV ventricle treated with radical tumor resection from 1982 through 1991. The purposes of this study were to identify the tumor origin and neural involvement, and to determine the natural history following surgical resection. Pathological studies showed that 18 were pilocytic astrocytomas (pure pilocytic in 12, mixed in 6), 2 fibrillary, and 1 gemistocytic. In the IV ventricle, 12 patients had a transependymal involvement of the floor (brain stem), 6 had an involvement of the wall (cerebellar peduncle), and 3 had involvement of both floor and wall. A gross total resection was performed in 9 patients, and the remaining 12 patients underwent a subtotal resection. All patients were followed without radiation therapy (RT) or chemotherapy. During a follow-up period of 6.5-15 years, all patients were alive. Eight patients suffered recurrence between five months and 66 months after diagnosis. Of these, five received RT for recurrence and had a complete response in all cases. The remaining 13 patients showed no evidence of disease and one had a stable residual tumor. The recurrence-free 5-year and 10-year survival rates were 62.5% and 57% respectively. Patients without brainstem involvement, with total resection, or with pure pilocytic astrocytoma had a better outcome than those with brain stem involvement, with subtotal resection, or with nonpilocytic or mixed histology. In summary, a great majority of benign IV ventricle astrocytomas involve the floor of the IV ventricle. It is often difficult to determine the origin of these tumors in most cases. Benign IV ventricle astrocytomas may not recur even after incomplete resection, and close observation without RT is recommended, although RT appears to be effective for these tumors when they recur.