A seroepidemiology survey of nine zoonoses was carried out in 2007 on 90 healthy adult volunteers in Viljujsk, a northern city in the Republic of Sakha (Eastern Siberia). The seroprevalence of Lyme borreliosis was 3.3% by immunofluorescence. None of the subjects displayed a positive enzyme-linked immunosorbent assay/Western blot result for alveolar or cystic echinococcosis. The seroprevalence of toxocariasis by Western blot was 4.4%, and 8.9% of the subjects had anti-Toxoplasma IgG. By enzyme-linked immunosorbent assay, the seroprevalence of trichinellosis was 4.4%. Three subjects were simultaneously positive for tick-borne encephalitis and West Nile infection, so no clear diagnostic conclusion could be reached for these flavivirus diseases. Interestingly, Crimea-Congo hemorrhagic fever had an 11.1% seroprevalence rate, indicating that Viljujsk is the most northern focus of this infection. Additionally, this finding suggests a potential involvement of Crimea-Congo hemorrhagic fever agent, or of another member of the Bunyaviridae family, in the genesis of the so-called Viljujsk encephalomyelitis.