Mental health problems can develop at any point in life and may be influenced by a variety of factors, including genetics or family history of a disorder, chemical imbalances in the brain, or stressors in the environment. Adolescence is a time of great change and transition, when youth are starting to make decisions about career paths, further schooling, and living on their own. These stressors, coupled with changing peer and family interactions, may lead in some cases to mental health problems, such as depression, suicidal thoughts, and anxiety disorders, particularly if the adolescent has a family history of mental illness. It is important for out-of-school time programs to be aware of these problems and to recognize their symptoms since mental health problems during adolescence can lead to other difficulties including substance use, school dropout, and antisocial behavior. This brief summarizes the signs and symptoms of depression, suicide risk, and anxiety disorders, and suggests research questions that can help screen or monitor mental health issues. It also provides resources for out-of-school time program practitioners on these topics. (Contains 11 endnotes.)