We evaluated the differences in motor control organization between parkinsonian patients with (seven cases) and without(ten cases) gait disorder. We used positron emission tomography (O-15-H2O-PET) to measure regional cerebral blood flow as a correlate for local neuronal activation. This has been assessed during repetitive joystick movements of the right hand, externally triggered using a metronome as an auditory cue. In patients with Parkinson's disease (PD) without gait disorder, the contralateral supplementary motor cortex and the bilateral cerebellum were activated, while in PD patients with gait disorder the contralateral Broca's area, the contralateral sensory motor cortex and the homolateral cerebellum were activated. Our results suggest that PD patients with gait disorder creates an internal verbal cue in order to control the output of the movement of joystick, supplying the loss of control of the supplementary motor cortex that is activated in patients without gait disorder.