Intrinsic brain stem tumors are a heterogeneous group of neoplasms that may be classified according to clinical and neurodiagnostic criteria. We have described simple anatomic categories that include focal, diffuse, cystic, and cervicomedullary tumors. Although there is no surgical option for the common diffuse brain stem neoplasms, the other tumors may be operated on if the clinical and neurodiagnostic assessment suggests the possibility of a benign neoplasm. It is important to emphasize that although all tumors that were covered by intact ependyma or pia were considered intrinsic tumors in this series, most of these tumors created a "bulge" that was obvious on visual inspection of the external surface of the brain stem. In all of the tumors that were benefitted by surgery, the neoplasms tended to "bulge" from the brain stem rather than infiltrate it, which was the case with the diffuse neoplasms. It seems likely that many of the focal, cystic, and cervicomedullary tumors are similar to the dorsal exophytic brain stem tumors, which are characteristically low-grade astrocytomas that disrupt the ependymal lining and grow posteriorly into the fourth ventricle. Although surgery has been well tolerated and beneficial in many patients, it would be premature to comment on the duration of remission or the possibility of permanent cure.