The obsessive compulsive disorder is characterized by persistent, repetitive, intrusive and senseless thoughts that “invade” the patient’s mind, which are also called obsessions. The person recognizes these thoughts as nonsense, inadequate or unnecessary but cannot control them. They may appear as repetition of words, thoughts, fears, numbers, pictures, or scenes and are usually linked to ideas of neatness, contamination, safety, aggression, or sex. A compulsion is a repetitive behavior (wash hands, organize, check) or a mental act (pray, count, repeat words, phrases, numbers) that the person is compelled to do because of an obsession. Compulsive behaviors are an attempt to avoid or reduce suffering due to an event or situation that could possibly cause such feelings. They are time consuming (over an hour a day) and interfere significantly in the daily routine and in the social, academic, and occupational life of the child or adolescent.

People with obsessive compulsive disorder can have obsessions, compulsions, or both. Children usually understand that their compulsions are unnecessary and meaningless. However, they have difficulty in resisting the behavior. In the case of young children, there may be compulsions without obsessions and these children cannot understand them as excessive and meaningless. Children usually hide their rituals until they are so intense that they are discovered. These symptoms tend to change as time goes by: some children develop checking and verification rituals, which may escalate into rituals of symmetry, for instance.