In the Sassman area, province of Halsingland, Sweden, mosquitoes were sampled in 1983 from aquatic habitats, overwintering sites, cattle sheds, human bait, with UV-light traps, rabbit-, guinea-pig-, hen-, dove- and unbaited suction traps and similarly baited net traps. Anopheles beklemishevi, An. messeae, Aedes cantans, Ae. cataphylla, Ae. cinereus, Ae. communis, Ae. diantaeus, Ae. excrucians, Ae. hexodontus, Ae. intrudens, Ae. leucomelas, Ae. pionips, Ae. punctor, Ae. vexans, Culex pipiens, Cx. torrentium, Cx. territans, Culiseta alaskaensis, Cs. bergrothi, Cs. morsitans, Cs. ochroptera and Mansonia richiardii were recorded as new to the province. Data are presented on the ecology including seasonal abundance and seasonal blood-feeding activity of each species. Ockelbo disease, caused by a virus indistinguishable from Sindbis virus, is prevalent amongst humans in the study area. The ecological and behavioral potential of species of Culex, Culiseta and Aedes to transmit the virus is discussed.