This paper reports results of the first wave of a two-wave panel survey carried out on a representative sample of Puerto Rican public and private secondary school students in the 1974--1975 academic year. Twelve percent of the students reported the use of one or more illicit drugs. The illicit drug most frequently used was marijuana. A greater proportion of adolescents have used alcohol and tobacco than any of the illegal drugs. Private school students of both sexes reported more use of illicit and licit drugs than their public school peers, suggesting that socio-economic factors may be influencing Puerto Rican adolescent drug behavior. Differences between Puerto Rican adolescents vary significantly depending on sex and suggest that Puerto Rican sociocultural conditions may have an important effect upon male-female drug use patterns. One of the most significant findings of the study is the high frequency of drug use among Puerto Rican adolescents who ever lived in other countries.