Mental disorders among children are described as "serious deviations from expected cognitive, social, and emotional development" (US Department of Health and Human Services Health Resources and Services Administration, Maternal and Child Health Bureau. Mental health: A report of the Surgeon General. Rockville, MD: US Department of Health and Human Services, Substance Abuse and Mental Health Services Administration, Center for Mental Health Services, and National Institutes of Health, National Institute of Mental Health; 1999). These disorders are an important public health issue in the United States because of their prevalence, early onset, and impact on the child, family, and community, with an estimated total annual cost of $247 billion. A total of 13%-20% of children living in the United States experience a mental disorder in a given year, and surveillance during 1994-2011 has shown the prevalence of these conditions to be increasing. Suicide, which can result from the interaction of mental disorders and other factors, was the second leading cause of death among children aged 12-17 years in 2010. Surveillance efforts are critical for documenting the impact of mental disorders and for informing policy, prevention, and resource allocation. This report summarizes information about ongoing federal surveillance systems that can provide estimates of the prevalence of mental disorders and indicators of mental health among children living in the United States, presents estimates of childhood mental disorders and indicators from these systems during 2005-2011, explains limitations, and identifies gaps in information while presenting strategies to bridge those gaps. Attention-deficit/hyperactivity disorder (6.8%) was the most prevalent parent-reported current diagnosis among children aged 3-17 years, followed by behavioral or conduct problems (3.5%), anxiety (3.0%), depression (2.1%), autism spectrum disorders (1.1%), and Tourette syndrome (0.2% among children aged 6-17 years). An estimated 4.7% of adolescents aged 12-17 years reported an illicit drug use disorder in the past year, 4.2% had an alcohol abuse disorder in the past year, and 2.8% had cigarette dependence in the past month. The overall suicide rate for persons aged 10-19 years was 4.5 suicides per 100,000 persons in 2010. Approximately 8% of adolescents aged 12-17 years reported ≥14 mentally unhealthy days in the past month. Future surveillance of mental disorders among children should include standard case definitions of mental disorders to ensure comparability and reliability of estimates across surveillance systems, better document the prevalence of mental disorders among preschool-age children, and include additional conditions such as specific anxiety disorders and bipolar disorder. Standard surveillance case definitions are needed to reliably categorize and count mental disorders among surveillance systems, which will provide a more complete picture of the prevalence of mental disorders among children. More comprehensive surveillance is needed to develop a public health approach that will both help prevent mental disorders and promote mental health among children.