Analysis of CT scans of 25 patients with cerebellar astrocytoma indicates that a typical spectrum of findings exists for the cerebellar astrocytomas. CT is highly accurate in delineation and characterization of new and recurrent tumors. Recurrences may be demonstrated long before symptoms occur. The density of the fluid in the tumor cyst is twice that of cerebrospinal fluid. Thus differentiation from nonneoplastic cystic lesions and postoperative defects is possible. CT findings of solid or cystic tumor frequently correlate with histologic categorization, and in such cases prognostic information can be derived from the CT appearance.