Epidemiologists have conducted nationwide surveys, such as the National Household Survey on Drug Abuse (NHSDA) and the National Comorbidity Survey (NCS), to estimate the prevalence of either the individual or the concurrent consumption of and dependence on alcohol and tobacco. These estimates indicated that for both alcohol and tobacco, use was already relatively high among the youngest respondents, peaked among young adults, and declined in older age groups. A similar pattern existed for concurrent alcohol and tobacco use. Moreover, these estimates showed only moderate gender differences. With respect to dependence, the age-related prevalence patterns differed somewhat for alcohol and tobacco, with the prevalence of tobacco dependence relatively lower among the youngest respondents compared with the prevalence of alcohol dependence. The age-related pattern for concurrent alcohol and tobacco dependence was similar to that found for tobacco dependence.