Cognitive dysfunction is a common symptom of Parkinson's disease (PD) that causes significant morbidity and mortality. The severity of these symptoms ranges from minor executive symptoms to frank dementia involving multiple domains. In the present review, we will concentrate on the aspects of cognitive impairment associated with prefrontal dopaminergic dysfunction, seen in non-demented patients with PD. These symptoms include executive dysfunction and disorders of thought, such as hallucinations and psychosis. Such symptoms may go on to predict dementia related to PD, which involves amnestic dysfunction and is typically seen later in the disease. Cognitive symptoms are associated with dysfunction in cholinergic circuits, in addition to the abnormalities in the prefrontal dopaminergic system. These circuits can be carefully studied and evaluated in PD, and could be leveraged to treat difficult clinical problems related to cognitive symptoms of PD.