Childhood and adolescent intrapersonal and interpersonal influences on older adolescents' drug use were examined with an interactional approach. Data were obtained when subjects were 5-10, 13-18, and 15-20 years old. Latent-variable confirmatory factor analysis was used to determine the fit of the variables to the latent constructs. Next, a structural model was hypothesized and tested to assess the influences of childhood and earlier adolescent factors on later adolescent drug use. Childhood aggression and parental sociopathy affected drug use in late adolescence. Unconventionality during early and middle adolescence had an important and pervasive impact on all aspects of middle and late adolescent functioning. Finally, both intrapersonal and interpersonal factors from childhood and early adolescence affected self-drug use during middle and late adolescence.