This invention provides methods utilizing ketamine for the treatment of motor disorders and/or side effects associated with certain medications used in the treatment of motor disorders. For example, in some embodiments, methods are provided for treating side effects associated with the administration of levodopa to a subject having Parkinson's disease, by administering a dose of ketamine or a pharmaceutically acceptable salt thereof. In particular, the invention provides methods for reducing dyskinesia associated with motor disorder (e.g., Parkinson's disease) treatments, and effective doses of ketamine or a pharmaceutically acceptable salt thereof.