Acute confusional state (ACS) and acute agitated delirium (AAD) after infarction in the right middle cerebral artery territory were investigated in 41 consecutive patients. Acute confusional state was diagnosed on the basis of the results of the Mini-Mental State Examination, and AAD was distinguished from ACS by the characteristic behavioral abnormality. Of these patients, 25 presented with ACS, and six with AAD. Acute confusional state and AAD are common syndromes after infarction of the right middle cerebral artery, and infarction in this territory, therefore, has an important clinical implication as a cause of these syndromes. Acute confusional state is a disorder in which cognitive and integrative functions become defective, reflecting disturbance of global attention, and is closely correlated with other right hemispheric global and directed attentional disorders. It is linked to damage to the right frontostriatal region and is associated with lesion volume. In comparison, AAD is a disorder in which emotional and affective components are predominantly altered. None of the right hemispheric behavioral syndromes correlated with AAD. It may be related to damage to the right middle temporal gyrus.