This analysis reviews the autopsy findings in 16 patients treated with irradiation for thalamic and brain stem tumors. The primary tumor site prior to treatment was the thalamus in six, midbrain in two, and the pons in eight. Histologic classification of the autopsy material revealed well-differentiated astrocytoma in two, astrocytoma with anaplasia in two, and glioblastoma multiforme in 12. Port film review showed recurrent/persistent tumor confined to the irradiated volume in 25% (4/16) and involved the field margin as a component of failure in 75% (12/16). Meningeal seeding to the spine occurred in 4/12 marginal failures. Tumor spread into adjoining structures involved the cerebellum in 10/12 marginal failures. None failed entirely outside the irradiated volume. Histologic classification could not be associated with extent of tumor at autopsy.