This study tests a multidimensional model of adolescent drug use. The model incorporates sociodemographic variables, personality variables (state and trait anxiety, depressive mood, and sensation seeking), cognitive variables (knowledge, attitudes, and intentions), interpersonal factors (relationships with peers and parents), and the availability of drugs. The model was tested in a longitudinal study, comprising two phases. A total of 1446 high school students served as subjects. The role of cognitive (attitudinal) and interpersonal factors (relationships with parents and peers) was confirmed. In addition, sensation seeking proved to have significant predictive power. Anxiety, depression, and sociodemographic factors, by contrast, had virtually no influence. Availability had a minor effect. The multidimensional explanation was validated longitudinally. The factors related to drug use at the first phase predicted use at the second. This multidimensional explanation accounted for the use of various substances, suggesting that different substances-whether legal or illegal-share a common multidimensional explanation.