Mental disorders are diagnosable conditions characterized by changes in thinking, mood, or behavior (or some combination of these) that can cause a person to feel stressed out and impair his or her ability to function. These disorders are common in adolescence. This "Adolescent Health Highlight" presents the warning signs of mental disorders; describes the types of mental disorders and their prevalence and trends; discusses the consequences and risk of mental disorders; presents treatment options and barriers to accessing mental health care; and provides mental health resources. (Contains 2 figures and 16 resources.)