Obsessive-compulsive disorder (OCD) is diagnosed when a teen has obsessions—recurrent, persistent, intrusive, anxiety-provoking thoughts, or compulsions—repetitive behaviors or rituals that they feel they must perform. For example, a person with OCD might wash their hands over and over or follow a step-by-step routine in getting dressed before school and, if one thing is done out of order, feel they must start over. OCD involves irrational behavior that interferes with normal life. For example, it may take the young person hours to get ready for school and can lead them to be late or miss school. Or it may take a lot of time to finish schoolwork because the teen feels as if she has to rewrite an assignment over and over again to get it just right.

People with OCD sometimes exhibit tics (like twitches and spasms) and attention deficit hyperactivity disorder (ADHD). Although OCD was once considered a rare condition, recent research suggests that as many as 1% of the population under 18 shows signs of this disorder.