The study sample included 1,303 adolescents in 7th and 8th grades, and the sample was restricted to black and Hispanic youth. Participating students provided data in surveys administered in 1994 during the 7th grade, 3 months later, and a year later during 8th grade. Survey items included measures of intra- and interpersonal functioning, as well as a variety of attitudes, intentions, and behaviors related to alcohol and marijuana use. Risk factor techniques were used to construct additive risk indexes that reflected key domains of a psychosocial model of deviant behavior. Cross-sectional analyses showed ethnic identity moderate the effects of alcohol-related expectancies, knowledge, and social skills for alcohol use, whereas ethnic identity moderated the effects of social influences, competence, and social skills for marijuana use. Longitudinal analyses indicated ethnic identity moderated the effects of social skills on alcohol use and in some instances uniquely predicted both alcohol and marijuana use, controlling for risk. Study findings are discussed in terms of the formative role of cultural factors as they shape vulnerability to adolescent alcohol and drug use. 60 references, 1 endnote, 4 tables, and 2 figures