Magnetic resonance brain scans were obtained from 10 chronic alcoholics within 2 weeks of alcohol withdrawal, and 19 to 28 days later. Age-matched control subjects were scanned at comparable intervals. At the initial scan, the alcoholics had larger lateral ventricles than the controls; at the second scan, their ventricles were significantly smaller than at the first scan. Among the controls, there was no mean change in the size of the lateral ventricles between the first and second scan. This study demonstrates reversibility in ventricular enlargement with short-term abstinence from alcohol. The role of rehydration in this process and the possibility of further changes with continued abstinence remain to be tested.