Three cases of proven herpes simplex encephalitis are reviewed from a pathologic point of view. The most severe lesions were in the cerebral cortex in which there were massive circumscribed areas characterized by necrosis, infiltration by large mononuclear cells, perivascular parenchymal accumulations of cells and neuronophagic nodules. Type A intranuclear inclusion bodies, best observed in hematoxylin and eosin prepns., were found in profusion in oligodendroglia and ganglion cells of the cerebral cortex and in oligodendroglia of the subcortical white matter.