The study objective was an attempt to explain uneven distribution of the incidence of tick-borne encephalitis (TBE) throughout the past two decades. A sharp rise was recorded in the last decade: while 2596 TBE cases were reported in the decade 1983–1992, as many as 5892 TBE cases were reported in the decade 1993–2002, with high rates persisting also in the following years (606 TBE cases reported in 2003). Data from the database TBE EPIDAT of the National Institute of Public Health, Prague, and that of the Communicable Diseases Information System, Ostrava,were used for analysis. Meteorological data were taken from the database of the Czech Institute of Hydrometeorology, Prague. In 1971 to 2003, 13 231 laboratory confirmed TBE cases were reported in the Czech Republic. Uneven distribution of these TBE cases in time is consistent with the observations of climate variation made between 1931 and 2000. The increase in the TBE incidence in the Czech Republic in the last decade was characterized by the following features: 1) higher rates of TBE cases manifested in regular TBE natural focuses, 2) reemergence of TBE in the same localities after 20 and more year intervals and 3) emergence of TBE in localities where it was not reported before. At the same time shifts in TBE seasonal trends (i.e. to March and October–November) were observed, associated with a TBE incidence peak in autumn. Field research revealed that the major factor are the climate-related changes in ecology of the TBE vector Ixodes ricinus and resulting variation in its population density.TBEemergence in newareas is linked to the occurrence of ticks Ixodes ricinus at higher altitudes (previously found at 700 m and currently spreading to 1200 m) as well as to a coming warm climate era.

        Key words: tick-borne encephalitis – tick Ixodes ricinus – climate.