The increasing prevalence of multiple drug use among adolescents presents researchers with complex conceptual and measurement issues. This work examines definitions of and indicators of multiple drug use involvement, as well as the interrelationships between indices of drug involvement incorporating different dimensions. Data regarding the relationship between patterns of alcohol use and illicit drug use in a population of 1473 teenagers interviewed in a northwestern metropolitan community indicate that: (1) regardless of the dimensions incorporated into four different indices of drug involvement examined, intercorrelations between indices were strong; (2) although the correlations between indices of drug involvement and overall levels of alcohol intake were uniformly weak, it was shown that levels of drug involvement vary directly with the maximum volume of alcohol used. Although the results of the current investigation must be viewed cautiously because of the concentration of heavy users of both alcohol and drugs in the population upon which the research is based, among adolescents, the spacing of drinking episodes and the patterning of alcohol intake may be more important determinants of polydrug involvement than the quantity of alcohol consumed.