This report presents the first information from the 2005 National Survey on Drug Use and Health (NSDUH), an annual survey of the civilian, noninstitutionalized population of the United States aged 12 years old or older. Prior to 2002, the survey name was the National Household Survey on Drug Abuse (NHSDA). This initial report on the 2005 data presents national estimates of rates of use, numbers of users, and other measures related to illicit drugs, alcohol, and tobacco products. Measures related to mental health problems also are presented, including data on depression and on the co-occurrence of substance use and mental health problems. Estimates from NSDUH for States and areas within States will be presented in separate reports. A major focus of this report is a comparison of substance use prevalence estimates between 2004 and 2005. Trends since 2002 also are discussed for some measures. Because of improvements to the survey in 2002, the 2002 data constitute a new baseline for tracking trends in substance use and other measures. Therefore, estimates from the 2002 through 2005 NSDUHs should not be compared with estimates from the 2001 and earlier surveys in the series to assess changes in substance use and mental health problems over time.