In this study, we aimed to examine the olfactory function of adolescents with obsessive-compulsive disorder (OCD). We investigated olfactory function of 50 adolescents with OCD and 50 healthy controls (min-max, 12-17 years) by the "Sniffin' Sticks" extended test. OCD and depression symptomatology were assessed with the Maudsley Obsessive-Compulsive Inventory (MOCI) and the Children's Depression Inventory (CDI). Adolescents with OCD had lower olfactory performance than healthy controls. The patients who responded positively to the treatment exhibited performance superior to the patients with partial response and those untreated. All olfactory measurements were significantly inversely correlated with MOCI and CDI total scores and OCD duration. Our results show that OCD has a significant impact on all olfactory tests, and olfactory impairment is related to symptom severity, duration, and course of OCD. The decrease in olfactory function may be a noninvasive state marker for OCD. Further investigations in longitudinal studies are required to confirm our results.