The study addressed the following questions: (1) How strong is the relationship between illicit drug use and other illegal activities? (2) Does illicit drug use lead to an increase or decrease in subsequent delinquency? (3) Does delinquency predict to later drug use? (4) Is illicit drug use associated with specific types of crimes? The initial sample was comprised of approximately 2,200 10th grade boys in 87 public schools and was obtained by using a random sampling procedure. Followup interviews were conducted in the spring of 1968, 1969, and 1970. Self-administered questionnaires were mailed out in the spring of 1974, 4 years after the majority of subjects had graduated from high school. A single composite measure of illicit drug use was constructed to examine relationships across time. Some of the findings of the study included: illicit drug use was related positively and strongly to other forms of illegal behavior; (2) the higher the degree of an individual's involvement with drugs, the higher was his expected level of delinquency, (3) crimes against property were considerably more related to illicit drug use than were crimes against persons; and (4) young men who used only marijuana were lower than the other drug-using groups on both indices of delinquency. No evidence was found of a lasting impact of drug use on delinquency levels, but some covariance was noted within the same 1-year interval for which drug use was measured. It can be concluded that nonaddictive use of illicit drugs does not seem to play much of a role in leading users to become more delinquent. In fact, it is more plausible to assume that delinquency leads to drug use. Ten tables of data interpretation and (6) references are included.