This study examined the reliability of quantitative measures of cerebral magnetic resonance images (MRI) in repeated scans. Ten subjects were scanned twice, at 2- to 4-week intervals. Volumetric data from 14 regions of the cerebrum, the caudate nucleus, and the lateral ventricles and area measures of the corpus callosum were acquired. Intrarater and scan-rescan reliabilities, including the relative percent error from each of these two sources, were determined for each structure. Intraclass correlations ranged from 0.88 for the head of the caudate nucleus to 0.99 for the ventricular volume. Quantitative cerebral MRI measures of these structures are stable over time intervals of 2-4 weeks.