The authors summarize the role of diagnostic classification in the treatment and research of AUDs and describe the current diagnostic criteria for AUDs as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV). Next, the article reviews epidemiological and clinical research on DSM-IV AUD criteria among adolescents and potential limitations of these criteria when applied to this age group. Further, the authors describe some of the diagnostic interviews and screening tools that can be used to assess AUDs among adolescents. The article notes that the diagnostic criteria for AUDs in the DSM-IV were developed largely from research and clinical experience with adults. Although the number of studies is small, the available data suggest important limitations of the DSM-IV AUD criteria when applied to adolescents. More research is needed to assess potential changes in diagnostic criteria that may better represent the nature and development of adolescent alcohol problems. It is an open question as to whether future changes in diagnostic criteria for AUDs can provide a unified system that is equally valid for both adults and adolescents, or whether adolescent-specific clinical and research criteria for AUDs should be developed. Research has generally supported the validity of self-reports of alcohol and other drug problems obtained from teenagers in clinical settings. Future research should identify characteristics of the individual adolescent and of the setting in which the information is obtained, since these factors influence the validity of self-reports. Clinicians and researchers have numerous options when selecting diagnostic instruments and screening measures for adolescent AUDs. Many of these instruments have favorable reliability and validity, and several reviews provide an overview to help guide the choice of an appropriate assessment instrument. An outline of screening instruments for adolescent alcohol use disorders is provided. 44 references