A predominant symptom of Parkinson's disease is akinesia and bradykinesia, slowing in the initiation and execution of voluntary movement. There has long been speculation as to whether cognitive processes undergo similar processes, but findings may be confounded by the frequent co-occurrence of dementia and/or depression. Mental rotation provides an internal or cognitive analogue of real movement, and enables us to determine the speed of such mental processes independent of any concurrent motor slowing in response initiation and execution. Medicated patients with Parkinson's disease who were free of dementia and depression were found to be able to mentally rotate alphanumeric or figural stimuli, with and without advance information as to the view (front or back) of a stick figure shortly to be shown, as rapidly as normal healthy controls. We conclude that cognitive processes involved in mental rotation are not necessarily slowed in Parkinson's disease.