We compared responses to questions about tobacco use and passive exposure to smoking with biological tests for cotinine in order to estimate tobacco-reporting validity in an epidemiological survey on drug use. Respondents identified via multistage sampling (n=627) completed household surveys that were administered using an Audio Computer-Assisted Self-Interview (ACASI) procedure. Following the survey, respondents were asked to participate in drug testing. Saliva (oral fluid) was used to screen for the presence of cotinine, a major metabolite of tobacco. Hair, urine, and oral fluid testing were used to detect the presence of illicit drugs such as amphetamines, cocaine, heroin, and marijuana. While underreporting of tobacco was relatively rare, estimates from this recent study suggest that it may be increasing over time. Even after adjusting for passive exposure, self-report sensitivity estimates were still well below the 90% level suggested in prior reviews. Underreporting of marijuana and race/ethnicity showed a strong association with underreporting of tobacco use, suggesting that factors associated with the underreporting of illicit substance use parallel those associated with the underreporting of tobacco use.