The objectives of this study, carried out in 1995, were to assess both licit and illicit substance use among rural male and female Costa Rican adolescents, and associated health, psychological, and psychosocial problems. A sample of 304 students from rural schools was randomly selected. The mean age for females was 14.7 years (S.D. = 1.71), and for males was 14.4 years (S.D. = 1.62). The data were collected using the Latin-American version of Drug Use Screening Inventory (DUSI). Results showed a high prevalence of past-year alcohol use for both males and females (56.6% and 47.4%, respectively), and a lower prevalence of past-year tobacco use (44.0% and 7.7%). There results also showed a low level of use of solvent inhalants and benzodiazepines. In terms of illicit drugs, males preferred cocaine and marijuana, while females only reported amphetamine use. An analysis of adolescent functioning showed differences among alcohol users and nonusers in behavior patterns and peer relationships. However, no significant differences were found regarding rebellion, depression, and social isolation. The implications of these results are discussed, along with the importance of enhancing prevention, as well as early detection and intervention.