Attention deficit hyperactivity disorder (ADHD) is observed in approximately 5.9-7.1% of children and adolescents. Atomoxetine is selective norepinephrine transporter inhibitor and an alternative to stimulants used to treat ADHD. An 11-year-old male patient was brought to the child psychiatry clinic with complaints of difficulty in sustaining attention, getting bored quickly, inability to complete tasks and activities, and forgetfulness. A diagnosis of “Attention Deficit and Hyperactivity Disorder, Predominantly Inattentive type’’ was made according to the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders IV (DSM IV) and long-acting methylphenidate treatment was started. Gastrointestinal side effects such as anorexia and nausea due to the drug occurred with 36 mg/day long-acting methylphenidate treatment and methylphenidate was discontinued. Atomoxetine treatment was started at 25 mg/day in the first week, 40 mg/day for 2 weeks and then 60 mg/day (1.2 mg/kg/day) maintenance. Obsessive-compulsive symptoms such as symmetry obsession, not being sure of having done something, and constant need for approval occurred after the use of 60 mg of atomoxetine per day. A diagnosis of ADHD + Obsessive-Compulsive Disorder (OCD) was made according to DSM IV-TR following a re-evaluation. We believe this case will contribute to the literature with the development of OCD following the use of atomoxetine

Keywords: Atomoxetine, Obsessive-compulsive disorder