Data were obtained from the Epidemiological Catchment Area study conducted at five U.S. sites from 1979 to 1985. The study sampled 20,000 members of the adult population; respondents were interviewed three times over a 1-year period. Responding adults were asked about 10 childhood behaviors and, if a behavior had occurred, the age at which it first occurred. The connection between conduct disorders and substance abuse was partially explained by the fact that youth with conduct problems are more likely than others to be exposed to illicit drugs. Adult respondents who used illicit drugs had more conduct problems as children and an earlier age of first drug use. Gender, unlike conduct problems, appeared to have little predictive value with regard to susceptibility to substance use and abuse. Further understanding of how conduct problems contribute to substance abuse will probably require information about how they influence adolescent social relationships and environments and how they contribute in adulthood to facilitate or inhibit the heavy use of psychoactive substances. 18 references, 10 tables and 4 figures.