SummaryClinical and pathological descriptions were made on the three cases of acute diffuse lymphocytic meningo‐encephalitis.Clinical pictures of all cases were super‐posable in almost all respects: acute onset of the illness, meningeal symptom such as headache and vomiting, convulsions, con‐fusional state and psychomotor restlessness which necessitated all patients being admitted to the psychiatric clinic. Pressure of CSF was elevated in two cases and pleo‐cytosis was noted. After the clinical course of about 4 weeks the patients died.Morphological picture of three cases was very slight in comparison with severe clinical symptoms and consisted of perivascular lymphocytic infiltration in the frontal, temporal and parietal cortex and a very slight microglial response as well as the involvement of meninges. In Case 1 glial nodules were noted in the midbrain and pons. These changes were milder in Case 2 and Case 3 than in Case 1.The diagnostic problems and the anatomical findings were discussed and it was suggested that our three cases were primary encep