NIMH, the National Institute on Alcohol Abuse and Alcoholism (NIAAA), and the National Institute on Drug Abuse (NIDA) supported the addition of a meeting on dimensional approaches to the series of meetings that the American Psychiatric Association is conducting in preparation for the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). This meeting, "Dimensional Approaches in Diagnostic Classification: A Critical Appraisal," was held over two days in July on the NIH campus. The meeting participants were asked to address the research evidence for a dimensional approach, consider an illustrative example of a dimensional approach linked to a categorical definition, and consider the advantages and drawbacks of the example for six disorder categories: substance use, mood, major psychoses, anxiety, externalizing child, and personality disorders. As part of the preparation for this meeting, more than 40 data sets were identified, analysis of which might contribute to illuminating the possibilities and challenges of a dimensional approach. For more information, please contact Dr. Jim Breiling.