The study concludes that the distinction between DSM-IV alcohol abuse and dependence based on severity can be improved by using an alternative diagnostic algorithm that considers all of the alcohol abuse and dependence symptoms conjointly. Although the DSM-IV diagnostic categories differ in severity of alcohol-use disorders (AUDs), there is substantial overlap and inconsistency in AUD severity across these categories. Item Response Theory-based AUD severity estimates suggest that many persons diagnosed with abuse have AUD severity greater than persons with alcohol dependence. Similarly, many persons who have some symptoms but do not qualify for a diagnosis have more severe AUDs than persons with a diagnosis of abuse. In addition, two alcohol-dependence items, “tolerance” and “larger/longer,” show differences in severity between samples. The study involved 5,587 adolescents between the ages of 12 and 18, who were recruited from adjudicated, clinical, and community samples. They were administered structured clinical interviews. Analyses then examined the severity of alcohol abuse and dependence symptoms as well as the severity of AUDs within the diagnostic categories created by the DSM-IV. 2 tables, 4 figures, and 41 references