Parkinson's disease (PD) is rightly recognized as one of the most common age-related diseases of the brain. Despite the well-known definition of PD as a movement disorder, a large amount of information has recently accumulated with the recognition of this disease as a heterogeneous multisystem disorder in which neurotransmitter systems (serotonergic, noradrenergic and cholinergic) play an important role. These neurotransmitters determine the severity of the non-motor signs of PD. The development of dementia in PD generates a heavy burden not only of an economic but also of a social nature. In this regard, over the past 30 years, scientists in this field of medicine have been conducting more and more research to identify the role and place of biomarkers in predicting the development of dementia in PD, which will also allow the development of preventive methods of correction at the early stages of cognitive impairment. This review article summarised the primary modern information regarding the aetiology and pathogenesis of cognitive disorders in PD.