Altered oscillatory brain activity in Alzheimer disease (AD) may reflect underlying neuropathological changes, and its characterization might lead to new diagnostic possibilities. The present study using quantitative magnetoencephalography was set up to examine power spectrum changes in AD patients, and their diagnostic strength. Whole-head 151-channel magnetoencephalography was recorded during an eyes-closed resting state. Magnetoencephalography channels were grouped in 10 cortical regions, and both global and regional relative power was analyzed for the commonly used frequency bands. Eighteen AD patients [mean age 72.1 years ± 5.6 (SD); 7 women; mean Mini Mental State Examination score 19.2, range: 13-25] and 18 healthy controls [mean age 69.1 ± 6.8 (SD), 11 women; mean Mini Mental State Examination score 29, range: 27-30] were recruited, controls being mainly spouses of patients. Relative power analysis showed significant differences in most frequency bands, particularly in the temporo-parietal regions, with some relation to Mini Mental State Examination scores. Greatest diagnostic accuracy was found in the beta band, especially in the right occipital area (sensitivity 94%, specificity 78%). Quantitative relative power analysis of magnetoencephalography recordings is able to show widespread abnormalities in oscillatory brain dynamics in AD patients. By analyzing distinct cortical regions, this study provides a more detailed topographical view of abnormal brain activity in AD. Copyright © 2008 American Clinical Neurophysiology Society.