Ixodes ricinus on domestic ruminants was sampled through a natural year at several points in the Basque country, north Spain. The sampling points were comprised of the different natural regions, according to climate and vegetation, into which the region is commonly divided. Both the immature and adult stages were collected on cattle and sheep at five of the eight collecting points, namely in areas with a medium elevation, mild summers and a medium to high annual rainfall. The adults of this tick showed a bimodal pattern of activity in some areas, while in others the pattern was unimodal. It was concluded that, because of the adequate climate, I. ricinus is widely distributed in the Basque country, with geographically close populations adapted to different, local, changing conditions.