OBJECTIVE To study the ability of magnetic resonance imaging to measure the volume of the amygdala and detect amygdala atrophy in patients with early Alzheimer's disease. METHODS Prospective case-control study and "blind" measurements. METHODS Subjects were ambulatory outpatients selected from an institutional practice in Paris, France. METHODS We studied 11 patients with probable Alzheimer's disease according to National Institute of Neurologic and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) and Consortium to Establish a Registry for Alzheimer's Disease (CERAD) inclusion and exclusion criteria, as well as six age-matched control subjects. METHODS None. METHODS A 1.5-T magnetic resonance imager was used to acquire the images. Two neuroradiologists independently and blindly measured the volume of the right and left amygdalas on high-resolution contiguous slices. In addition, other cerebral structures, ie, the sylvian fissures, temporal lobes, lateral and third ventricles, corpus callosum, and hippocampal formation, were measured on a single slice. RESULTS The values obtained by the two observers correlated highly (r = .90), and interrater variability was 13%. The Alzheimer's disease group showed significant (33%, P < .0001) atrophy of the amygdala when compared with the control group. The other structures showed less variation. CONCLUSIONS Significant amygdala atrophy can be detected in vivo in patients with early Alzheimer's disease by means of standard magnetic resonance imaging. This technique may be useful in the early diagnosis of Alzheimer's disease.