Current research on thalamic lesions, especially on the speech and mental function leaves many questions still unsettled. We report here a case of aphasia and reduced mental function resulting from bilateral thalamic infarction. A 65-year-old man who had suffered from atrial flutter, suddenly presented neurological signs characterized by disorientation and aphasia, and he was confirmed to have bilateral small infarction of the anterior thalamic by CT scans. Three months later, the aphasia improved but severe disturbance of recent memory and reduced mental activity remained. One year after the onset, his verbal IQ improved to nearly 90 and his activity of daily life was moderate. However, marked reduction of recent memory, character change, and disorientation of place, time and person still persisted.     Even two years after the onset, his mental function was proved to be unchanged by examinations, which seemed to show the difficulty in amelioration of recent memory and mental function in the case of bilateral thalamic lesions.     We supposed that the mental deterioration was attributed to the reduced fiber connection between the frontal cortex and bilateral thalamic, and that the transient aphasia was due to the affection of the left thalamus and its surrounding portion.