Objective. To study clinical, diagnostic and epidemiological aspects of the «transitional form» of Parkinson’s disease (PD) in the Yaroslavl region. Material and methods. The study included the main group of patients (n=11) with a «transitional» form of PD, comparison groups (15 patients with essential tremor (ET), 15 patients with PD) and healthy individuals (n=15). Diagnostic criteria of MDS ET were used. PD was diagnosed by criteria of The Parkinson’s UK Brain Bank. The following scales were administered: UPDRS, HOEHN and YAHR, MMSE), PDQ-39, EUROQOL part 2, STAI, HDRS. Results and conclusion. The period of 15.7±5.8 years, characterized by bilateral postural-kinetic tremor, preceded the appearance of signs of parkinsonism in the «transitional» form of PD. This form of PD was characterized by slow progression, lack of cognitive and depressive disorders and less severity of anxiety disorders. In most cases, there was a head tremor (63.6%), a positive family history of ET in two generations (100%), the onset of parkinsonism from the left extremities (81.8%). The frequency of hyposmia was comparable to patients with PD. Quality of life indicators were significantly higher compared to PD patients. A genetic predisposition, which subsequently affects the development of parkinsonism, probably, underlies a rare phenotype associated with the transformation of ET into PDis.