This report presents results pertaining to mental health from the 2010 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. This report presents national estimates of the prevalence of past year mental disorders and past year mental health service utilization for youths aged 12 to 17 and adults aged 18 or older. Among adults, estimates presented include rates and numbers of persons with any mental illness (AMI), serious mental illness (SMI), suicidal thoughts and behavior, major depressive episode (MDE), treatment for depression (among adults with MDE), and mental health service utilization. Estimates presented in this report for youths include MDE, treatment for depression (among youths with MDE), and mental health service utilization. Measures related to the co-occurrence of mental disorders with substance use or with substance use disorders also are presented for both adults and youths. The report focuses mainly on trends between 2009 and 2010 and differences across population subgroups in 2010. Findings include: (1) In 2010, there were an estimated 45.9 million adults aged 18 or older in the United States with any mental illness (AMI) in the past year. This represents 20.0 percent of all adults in this country. Among adults aged 18 or older in 2010, the percentage having serious mental illness (SMI) in the past year was 5.0 percent (11.4 million adults); (2) Women aged 18 or older were more likely than men aged 18 or older to have past year AMI (23.0 vs. 16.8 percent) and SMI (6.5 vs. 3.4 percent); (3) In 2010, an estimated 8.7 million adults (3.8 percent) aged 18 or older had serious thoughts of suicide in the past year. Among adults aged 18 or older, 2.5 million (1.1 percent) made suicide plans in the past year, and 1.1 million (0.5 percent) attempted suicide in the past year; (4) Among the 45.9 million adults aged 18 or older with AMI in the past year, 20.0 percent (9.2 million adults) met criteria for substance dependence or abuse in that period compared with 6.1 percent (11.2 million adults) among those who did not have mental illness in the past year. Among the 11.4 million adults aged 18 or older with SMI in the past year, 25.2 percent also had past year substance dependence or abuse compared with 6.1 percent of adults who did not have mental illness; (5) In 2010, 31.3 million adults (13.7 percent of the population 18 years or older) received mental health services during the past 12 months; (6) Among the 45.9 million adults aged 18 or older with AMI in 2010, 17.9 million (39.2 percent) received mental health services in the past year. Among the 11.4 million adults aged 18 or older with SMI in 2010, 6.9 million (60.8 percent) received mental health services in the past year; (7) Among the 2.9 million adults aged 18 or older in 2010 with both SMI and substance dependence or abuse in the past year, 64.0 percent received substance use treatment at a specialty facility or mental health treatment in that period. Included in the 64.0 percent are 14.5 percent who received both mental health treatment and specialty substance use treatment, 45.0 percent who received mental health treatment only, and 4.3 percent who received specialty substance use treatment only; (8) In 2010, there were 1.9 million youths (8.0 percent of the population aged 12 to 17) who had major depressive episode (MDE) during the past year. Among youths aged 12 to 17 in 2010 who had past year MDE, 37.2 percent used illicit drugs in the past year compared with 17.8 percent among youths who did not have past year MDE; and (9) In 2010, 2.9 million youths aged 12 to 17 (12.2 percent) received treatment or counseling for problems with emotions or behavior in a specialty mental health setting (inpatient or outpatient care). The most common reason for receiving specialty mental health services among youths was feeling depressed (47.6 percent). Appended are: (1) Description of the Survey; (2) Statistical Methods and Measurement; (3) Other Sources of Mental Health Data; (4) References; and (5) List of Contributors. (Contains 35 figures, 6 tables and 23 footnotes.)