28 autopsy cases were investigated in which the thalamus was impaired in early life, i.e. prenatal, perinatal, and postnatal (under 1 year of age). The thalamus is vulnerable to brain damage in the perinatal and early postnatal period. Lesions in the thalamus are severe in the DM, PL and VPL, and moderate in the VL and pulvinar thalamus. The anterior nuclei and center median show little change. Many of the cases with .athetoid movements have complicated thalamic lesions in addition to those of the basal ganglia. In one patient who showed athetosis as a sequela of encephalitis japonica, the VL and PL in the thalamus were involved severely; in contrast the basal ganglia revealed very slight changes.