Nucleotide sequencing was used to characterize unidentified California (CAL) serogroup virus isolates from Russia. These viruses were isolated from mosquitoes and humans during epidemiologic investigations on the role of CAL serogroup viruses in the increased incidence of arboviral encephalitis in Russia. Most of the isolates were identified serologically as snowshoe hare (SSH), Inkoo (INK), and Tahyna (TAH) viruses, but some of the isolates were difficult to classify serologically, suggesting that they could be reassortant viruses. There is evidence that at least 2 of these viruses are not reassortant viruses. Sequence analysis revealed that the Russian viruses differ from other Eurasian and North American CAL serogroup viruses in all of the segments analyzed. They are most closely related to SSH virus. Whether they differ sufficiently to be considered a new group of SSH-like viruses remains to be determined.