We evaluated the relationship between periventricular white matter lesions (PWMLs) and EEG abnormalities in probable Alzheimer's disease (AD). We visually analyzed the EEG of 27 probable AD patients with mild to moderate degree of cognitive impairment participating in a longitudinal study of dementia. Patients had both CT and MRI scans performed at baseline examination, which also included an EEG. PWMLs were rated in CT and MRI films using a semiquantitative method. The EEGs were classified according to the Mayo Clinic Classification System. Abnormal EEGs correlated with PWMLs rating scores were detected on CT, but not on MRI. These data suggest that the presence of PWMLs contribute to the abnormal EEGs observed in AD patients, and that white matter abnormalities in CT correlate better with both the clinical findings and EEG than does the more sensitive but less specific MRI.