Objective: To assess the sensitivity and specificity of linear measures of brain atrophy in the diagnosis of Alzheimer disease (AD) in the early stages. Methods: Linear measures of regional frontal lobe (bifrontal index, interhemispheric fissure width), medial temporal lobe (interuncal distance, minimal thickness of the medial temporal lobe), and hippocampus (hippocampal height, width of the choroid fissure, width of the temporal horn and distance between the hippocampus and brain stem), indicating the indeces of brain atrophy were made on the magnified MRI obtained in 30 patients with mild AD, 20 patients with multi-infarct dementia (MID) and 20 control subjects. Results: The measure with the best sensitivity in discriminating AD patients from MID and control subjects was the width of the temporal horn, the sensitivity being 90% and the specificity being 85%. A compound measure of the width of the temporal horn, the width of the choroid fissure; the interuncal distance, the hippocampal height and the distance between the hippocampus and brain stem could discriminate the patients with mild AD from MID and the control subjects with 93% sensitivity and 95% specificity. Conclusion: Linear measures of hippocampal atrophy can be of use in the routine diagnosis of AD, even in its early stages.