To identify those patients most likely to benefit from a cerebral biopsy to diagnose dementia, we reviewed a series of 14 unselected biopsies performed during a 9-year period (1980 through 1989) at Duke University Medical Center, Durham, NC. Pathognomonic features allowed a definitive diagnosis in seven specimens. Nondiagnostic abnormalities but not diagnostic neuropathologic changes were seen in five additional specimens, and two specimens were normal. Creutzfeldt-Jakob disease was the most frequent diagnosis. One patient each was diagnosed as having Alzheimer's disease, diffuse Lewy body disease, adult-onset Niemann-Pick disease, and anaplastic astrocytoma. We conclude that a substantial proportion of patients presenting clinically with atypical dementia are likely to receive a definitive diagnosis from a cerebral biopsy. However, in those with coexisting hemiparesis, chorea, athetosis, or lower motor neuron signs, cerebral biopsies are less likely to be diagnostic.