Traditionally, Parkinson’s disease is associated with a deficit of dopaminergic system, manifested in the extrapyramidal motor disorders. In addition, the disease is characterized by a wide variety of not movement disorders. For example, the spectrum of autonomic, mental, cognitive and sensory symptoms is presented. Cognitive impairment, including mild cognitive impairment and dementia in Parkinson’s disease are among the most common disorders are not motor. The purpose of this study was aimed to investigate the relationship of early cognitive impairment and rate of glucose metabolism in different parts of the brain in patients with Parkinson’s disease. Positron emission tomography (PET) with fluorodeoxyglucose synthesis in patients suffering from Parkinson’s disease was performed. Study group consisted of patients (31 persons, age 41-77 years). Patients have passed inpatient and/or outpatient treatment at the clinic of the Institute of Human Brain of the Russian Academy of Sciences. The control group (15 persons) consisted of patients of similar age group without cognitive impairment. To estimate the rate of glucose metabolism was used an original technique of the Institute of Human Brain. Immediately prior to the intravenous administration of radiopharmaceutical [18F]-deoxyglucose was synthesized. Psychological testing consisted of a clinical interview, observation, survey, test, as described in a brief assessment of mental status (MMSE) and the battery frontal dysfunction (BFD). The study found that when the initial cognitive impairment observed pattern of changes in the rate of metabolism of glucose, characteristic of patients with severe cognitive impairment in Parkinson’s disease. This fact leads to the assumption of a high validity of the test battery frontal dysfunction for early diagnosis of cognitive impairment in Parkinson’s disease.