Since bluetongue outbreaks occurred in november 2007 in northern Spain, an intensive trapping program was carried out to study the diversity and abundance of the Culicoides Latreille (Diptera: Ceratopogonidae) species. Eleven sheep farms and seven natural habitats distributed throughout the Basque country region were sampled using UV light CDC traps between 2008-2011. A total of 348,685 Culicoides specimens belonging to 52 species were collected during 1,480 trappings in 24h periods. An updated checklist of these 52 species (including four new records for the Iberian peninsula) is provided from the Basque country. The most abundant species in sheep farms were the two sibling species of the obsoletus complex (81.8% of the total catches): C. obsoletus (Meigen) and C. scoticus Downes and Kettle. Culicoides lupicaris Downes and Kattle was the next most abundant taxon collected in farms (9.7% of the total). Few specimens of Culicoides imicola Kieffer, the bluetongue vector in Mediterranean Basin and some specimens of Culicoides nubeculosus (Meigen), an important candidate of BTV transmission were collected in northeast and northwest farms, respectively. In natural ecosystems, three species, Culicoides festivipennis Kieffer, Culicoides alazanicus Dzhafarov and Culicoides brunnicans Edwards, comprised 48.5% of the total captures. Culicoides obsoletus/C. scoticus was present throughout the year and even during the winter days in temperate Atlantic areas (Gipuzkoa, Biscay) whereas no catches occurred in winter at the southern farms of Alava, where the climate is much colder in that season. The majority of the species were active from March to November with maximum peaks of catches in summer. Most Culicoides obsoletus/C. scoticus specimens were collected outdoors (65.9%). The study shows greater occurrence and abundance of obsoletus and pulicaris complex in sheep farms and in lesser extent in natural ecosystems. Data about diversity, distribution and seasonal dynamics are als