This study objectively analyzed postural instability and cognitive function in patients with Parkinson's disease (PD) and a group of healthy elderly and middle-aged individuals. The study included ten healthy middle-aged individuals (range 42-57years), 14 healthy elderly individuals (range 60-90years) and 15 PD patients (range 58-93years). Center of pressure (COP) parameters were determined by means of computed static posturography during free standing with open and closed eyes. The level of cognitive functioning was examined with mini mental state examination (MMSE) and counting backwards test (CBT). Parkinson's disease patients showed significantly lower MMSE scores compared to healthy middle-aged (p=0.004) and elderly individuals (p=0.03). Mean duration of CBT in PD patients was significantly longer than in healthy subjects. COP parameters correlated with age of subjects and cognitive function (MMSE score). No significant differences in any stabilographic parameters were observed between healthy elderly subjects and PD patients. Age is the most significant factor impacting upon the static balance of older individuals during free standing. Compared to middle-aged and elderly individuals without central nervous system impairment, patients with PD present with significant delay in cognitive processes associated with executive function.