Methylphenidate (MPH) is a central nervous system stimulant derived from an amphetamine and acts as a potent inhibitor of catecholamine reuptake and increases dopamine levels in the brain. Methylphenidate is widely used for the treatment of children and adults with attention deficit hyperactivity disorder. Because the dopaminergic system is critical to the pathological process in Parkinson disease (PD), it has been suggested that MPH, which increases dopaminergic stimulation at the postsynaptic receptor level, may provide symptomatic relief in PD patients. This article reviews those studies that have evaluated the potential of MPH to treat the motor and cognitive aspects of PD, summarizes the evidence for clinical use in other neurological diseases, and briefly reviews the physiological mechanisms whereby MPH may bring about its therapeutic effects. Methylphenidate does seem to be useful for ameliorating cognitive, affective, and motor deficits in PD and in other neurological patients; however, additional studies are needed before MPH can be routinely prescribed as an adjunct therapy in these populations.