A 46-year-old man who developed progressive dementia after repeated head trauma was reported. At the age of 30 and 36, he encountered traffic accidents and suffered from blows to his head. At 37 years old, he noticed impairment of memory and comprehension. At 41 years old, he was observed to become easily angered. These symptoms were slowly progressive, and at age 46 he was examined by us. He had no particular family history of dementia. Neurological examination revealed a disturbance of cognitive ability. The brain CT and MRI showed marked atrophy of the cerebral cortex, especially in the frontal and temporal lobes without any demonstrable lesions in the white matter. A single photon emission computed tomography (SPECT) using inhalation of 133Xenon disclosed hypoperfusion of the cerebral blood flow localized in the bilateral frontal and parietal lobes. He was supposed to suffer from juvenile Alzheimer's disease which might have developed after repeated head trauma. One similar case had been reported as a posttraumatic premature Alzheimer's disease. Finally, we discussed other causes of dementia including metabolic, infectious and vascular diseases. The present case also suggests that head trauma might be one of the provoking or promoting factors of Alzheimer's disease.