A chromosomal and morphological study of the black flies of northern Sweden revealed six genera and 47 species, of which 12 species represent new records for the country. The total number of species now recorded from Sweden is 61. Cnephia eremites is recorded from the Palearctic Region for the first time. New chromosomal information is provided for about 40% of the species in northern Sweden. A lectotype is designated for Simulium annulitarse which is shown to be a member of the S. tuberosum species group. The northern Swedish fauna is dominated by the genus Simulium (81 %) and by mammalophilic species (49%). Approximately 34% of the species in northern Sweden have a Holarctic distribution.