The present study uses large nationally representative samples of high school seniors to explore whether the often large racial/ethnic differences in cigarette, alcohol, marijuana, and cocaine use may be attributable to racial/ethnic differences in background and/or in important lifestyle factors. The results indicate that controlling for background alone does not account for most racial/ethnic differences in drug use. In fact, if black youth were as likely as white youth to live in two-parent households and have highly educated parents, their drug use might be even lower than reported. Controlling for background alone does reduce Native American's relatively high drug use, suggesting that their level of use may be linked to their disadvantaged socioeconomic status. When both background and lifestyle factors are controlled, many of the racial/ethnic differences in drug use are considerably reduced or eliminated. Several lifestyle factors--including educational values and behaviors, religious commitment, and time spent in peer-oriented activities--strongly relate to drug use and help to explain the subgroup differences. The authors conclude by discussing theoretical and policy implications of this research, along with directions for future efforts. 48 references, 5 tables, and 1 figure (Author abstract)