Twenty-two patients with Parkinson's disease (PD) were studied by clinical evaluation, assessments of dementia and depression, as well as electrophysiologic examinations for blink reflex (BR), cortical somatosensory evoked potentials (CSEP), brain stem, and long-latency auditory evoked potentials (BAEP, and LAEP), and cerebrospinal fluid (CSF) assays for monoamine metabolites. Results show that PD patients have a significant decrease of Mini-Mental State Examination (MMSE) scores ( p < 0.05) and an increase of Hamilton Depression Scale (HDS) scores ( p < 0.01), as well as a longer latencies of R2 in BR, N19 and P22 in CSEP, W4 and W5 in BAEP and P300 in LAEP ( p < 0.01), and lower CSF levels of HVA and MHPG ( p < 0.05). The findings suggest a correlation between dementia/depression and mesocorticolimbic and mesostriatocortic dysfunction with dopaminergic and noradrenergic deficiencies in PD patients. Furthermore, parkinsonian dementia parallels the length of duration of the disease, but not the severity of motor disability. Parkinsonian depression parallels both the length of duration of the disease and the severity of motor disability.