The Alcohol Use Disorders Identification Test (AUDIT) is a 10-item questionnaire designed by the World Health Organization to screen for hazardous alcohol intake in primary health care settings. In this longitudinal study we examined its performance in predicting alcohol-related harm over the full range of its scores using receiver operating characteristic analyses. Three hundred and thirty ambulatory care patients were interviewed using a detailed assessment schedule which included the AUDIT questions. After 2-3 years, subjects were reviewed and their experience of alcohol-related medical and social harm assessed by interview and perusal of medical records. AUDIT was a good predictor of both alcohol-related social and medical problems. Cut-off points of 7-8 maximized discrimination in the prediction of trauma and hypertension. Higher cut-offs (12 and 22) provided better discrimination in the prediction of alcohol-related social problems and of liver disease or gastrointestinal bleeding, but high specificity was offset by reduced sensitivity. We conclude that the recommended cut-off score of eight is a reasonable approximation to the optimal for a variety of endpoints.