This report combines data from three large national surveys -- the 1991, 1992, and 1993 NHSDA's -- to estimate the prevalence of substance use, alcohol dependence, and need for illicit drug abuse treatment within 11 racial/ethnic subgroups. The subgroups are Native Americans, Asian/Pacific Islanders, non-Hispanic blacks, non-Hispanic whites, and seven subgroups of Hispanics: Caribbeans, Central Americans, Cubans, Mexicans, Puerto Ricans, South Americans, and "other Hispanics." The sample size of more than 87,000 respondents allows the analysis of racial/ethnic differences in substance use while statistically controlling for many sociodemographic characteristics, including age, gender, educational attainment, employment status, and family income. The report supports previous research in showing that although Asian/Pacific Islanders' substance use, alcohol dependence, and need for illicit substance abuse treatment are prevalent enough to warrant attention, they are low relative to those of the total U.S. population. Hispanic subgroups vary markedly in their substance abuse, alcohol dependence, and need for illicit drug abuse treatment, with Mexicans, and Puerto Ricans having the highest substance abuse. The report supports previous research in finding that Native Americans have a very high prevalence of past-year substance abuse. The report concludes that sociodemographic differences among racial/ethnic subgroups explain, at least in part, the subgroups' differences in prevalence of substance use, alcohol dependence, and need for illicit drug abuse treatment. 46 tables, 84 references, and appended methodology information