A total of 135 polioviruses (PV), including 25 wild and 110 vaccine-related, isolated in Belarus in 1957-1999 were studied by the analysis of the polymorphism of the restriction fragments lengths of two distal regions of the genome: the region (480 oligonucleotide pairs) coding the N-terminal fragment of capsid protein VP1 (RLFP-1) and the region (291 oligonucleotide pairs) coding the N-terminal fragment of nonstructural protein of 3D-polymerase (RLFP-3D1). The genetic analysis of the viruses made it possible to determine 3 epidemiologically different periods of PV circulation: (1) the prevaccination period (1957-1959) when wild PV of all 3 serotypes circulated on the territory of Belarus; (2) the early period of the use of Oral Poliomielytis Vaccine (1960-1966), characterized by simultaneous circulation of wild and vaccine PV, as well as vaccine/wild recombinant PV; (3) the period of the elimination of wild PV of indigenous origin and the circulation of vaccine-related viruses (1967-1999). The characteristic feature of wild PV was their pronounced genetic variability. 8 genetic variants of PV1, including 4 genetic groups, 2 genetic variants of PV2 and 1 genetic variant of PV3 were detected; 2 vaccine/wild recombinant PV were detected in 1960 and 1966. More than 40% of the vaccine-related PV under study had altered genetic characteristics (mutations and/or recombinations. Reverse variability, linked with the loss of a number of signs of attenuation, was shown to be characteristic of vaccine PV1. Recombinants occurred most frequently among PV3 (44.9%) and PV2 (40.0%), their recombinations being formed mainly with PV1. Recombinants PV2/PV1 and PV3/PV1 were found to have high frequency of reversion in the "PV1" fragment of the genome; this frequency exceeded that in PV1 with the homotypical genome (66.7 and 44.4% in contrast to 12.5%).