The authors studied 34 subjects with probable dementia of the Alzheimer type (DAT) and 28 healthy, age-matched control subjects, using a 1.5-tesla GE MRI scanner. Absolute volumes of ventricular and sulcal cerebrospinal fluid spaces and volumes, corrected for total intracranial volume, were significantly higher (P < 0.01) in the DAT group, compared to the control group. Right-left measures of hemispheric structural asymmetry were greater in the DAT group, whereas aging alone influenced brain structure in the control group. Also, in the DAT group, certain volumetric measures were significantly correlated with specific clinical indicators of severity of illness and some neuropsychological indices. These data demonstrate widespread structural abnormalities in relatively early DAT and a relationship between brain structure and some measures of cognitive dysfunction.