The neuroanatomical model involved in the pathophysiology of obsessive-compulsive disorder (OCD) postulates a hyperactivation of orbitofrontal, limbic, and basal ganglia circuits. We report a case of OCD secondary to brain dysgerminoma affecting this circuit in an adolescent who responded to citalopram. The patient is a 16-year-old-boy with a midline germinal tumor (dysgerminoma) affecting the caudate nuclei; left lenticular, right internal capsule's genu; and bilateral involvement of the interventricular septum close to the interventricular foramina. He had OCD symptoms and elevated tumor markers when he had a tumor relapse, and fluorodeoxyglucose positron emission tomography showed caudate nuclei involvement. He responded to citalopram that had to be titrated gradually to 80 mg/day.