College students (N = 161) were asked via a self-administered questionnaire about their frequency of drug use, duration of drug use, and sale of drugs to others for six categories of illicit psychoactive drugs. These items were combined to yield four indices of illicit drug involvement: frequency of marijuana use, total number of illicit drugs used, a Guttman scale of dichotomous items representing use vs nonuse in the six categories, and a summative index based on three related dimensions of drug involvement. Results indicated that all four indices were substantially related, suggesting that researchers can have confidence in the comparability of findings generated in past studies of college drug use using different drug-rating scales.