We report the pathological accuracy of image-directed stereotactic brain biopsy in 30 patients who had mass lesions of the brain and subsequently underwent resection of the mass. The histological diagnosis at stereotactic biopsy was appropriate for direction of clinical management in 28 of 30 patients. Correlation between the stereotactic and resection diagnoses was exact in 19 of 30 cases. These included 11 of 12 nonastrocytic neoplasms and 8 of 13 astrocytic neoplasms. Correlation was imperfect in 9 of 30 cases, but not to the extent of having significant clinical impact. These included 2 cases of anaplastic astrocytoma that were upgraded to glioblastoma multiforme, 2 cases of astrocytoma that had a significant oligodendroglial component, and 5 non-neoplastic lesions that were reported on biopsy as showing nonspecific reactive changes. In 2 of 30 patients, the stereotactic biopsy was not accurate. This included one patient who had glioblastoma multiforme whose stereotactic biopsy showed only necrotic tissue. Serious diagnostic error that resulted in clinical mismanagement occurred in one patient who had a pineal germinoma that had large areas of granulomatous inflammation at which the stereotactic biopsy was directed. This study provides evidence that, with careful target placement, stereotactic biopsy can provide biopsy material that represents the entire lesion with an accuracy that is sufficient for clinical management.