Drug abusers have historically tended to abuse more than one drug. However, over the past 5 years there has been an increasing tendency to combine narcotics, alcohol, sedatives, and/or stimulants. The statistical increase of such abuse in the United States is documented by national surveys and the findings of drug treatment programs and detoxification centers. To clarify the confusion about such terms as‘polydrug abuse’and‘multidrug abuse,’these terms are defined. A classification of multiple drug abuse is presented which demonstrates recent increases in each of four categories.