Purpose: To review the reliability and validity of the CAGE questionnaire across different patient populations and discuss its role in the detection of alcohol-related problems. Methods: The Cochrane Database for Systematic Reviews, Medline, Embase, and Psychinfo were searched. No systematic reviews were found on the Cochrane Database. Search of the other databases yielded one systematic review and one meta-analysis, on different aspects of CAGE. Three articles on reliability and 16 on validity of CAGE were found and used. Studies generally yielded Level II evidence. Results: CAGE has demonstrated high test-retest reliability (0.80-0.95), and adequate correlations (0.48-0.70) with other screening instruments. The questionnaire is a valid tool for detecting alcohol abuse and dependence in medical and surgical inpatients, ambulatory medical patients, and psychiatric inpatients (average sensitivity 0.71, specificity 0.90). Its performance in primary care patients has been varied, while it has not performed well in white women, prenatal women, and college students. Furthermore, it is not an appropriate screening test for less severe forms of drinking. Conclusions: CAGE is short, feasible to use, and easily applied in clinical practice. However, users should be aware of its limitations when interpreting the results. A positive screen should be followed by a proper diagnostic evaluation using standard clinical criteria.