OBJECTIVE: This study investigated whether attention-deficit hyperactivity disorder (ADHD) has an olfactory dysfunction and, if so, the effect of methylphenidate on this condition. METHODS: The "Sniffin" Sticks Test and a questionnaire were applied to 50 children with ADHD and 50 healthy children as the control group before and after being treated with methylphenidate. RESULTS: There was a statistical difference between ADHD and control groups in odor sensitivity, odor discrimination skills, and odor identification tests ( CONCLUSIONS: Although the sense of smell test in our study suggests that it may be a biological marker for diagnosing ADHD, treatment efficacy, and follow-up, further studies need to be conducted in more extensive series and with similar equipment.