A case of neuro-Behçet's disease with dementia and personality changes is described with magnetic resonance imaging (MRI), single photon emission tomography (SPECT) and neuropathological findings. MRI disclosed high signal areas in the cerebral white matter and the brain stem. SPECT showed a marked reduction of blood flow in the frontal cortex. Neuropathologically, multifocal necrotizing lesions with perivascular lymphocytic infiltration and glial proliferation were detected mainly in the brain stem, namely the midbrain and the pons. From these findings, it is suggested that mental disorders of neuro-Behçet's disease are related to the secondary dysfunction of the frontal cortex due to the damage of the subcortical structures, mainly the brain stem.