The clinical features of Hashimoto's encephalopathy have been attributed to a cerebral vasculitis, but pathologic material is rarely available. The authors describe an individual with Hashimoto's encephalopathy complicated by fatal status epilepticus. Postmortem examination demonstrated mild perivascular lymphocytic infiltration throughout the brain and leptomeninges plus diffuse gliosis of gray matter in the cortex, basal ganglia, thalami, hippocampi, and, to a lesser extent, the parenchymal white matter.