The internal classification of subgenus Culex is in a chaotic condition. The subgenus has only been examined on a worldwide basis by Edwards (1932), who divided it into two groups: the Sitiens Group (Old World) and the Pipiens Group (cosmopolitan). Both groups are highly complex assemblages and include species that do not readily fit into either group. Three additional species groups have been recognised subsequently: the Guiarti Group (Edwards, 1941) for several Afrotropical species, the Atriceps Group (Belkin, 1962) for three South Pacific species and the Duttoni Group (Harbach, 1988) for the unusual Afrotropical Cx. duttoni and Cx. watti. Heinemann & Belkin (1977, and later publications) recognised two groups in the Neotropical Region, the Declarator and Inflictus Groups, but did not indicate which species they include. Strickman (1990) made reference to the Declarator Group, but he also did not mention which species comprise the group. The internal classification of the subgenus presented here is based principally on information extracted and integrated from the works of Edwards (1932, 1941), Belkin (1962), Forattini (1965), Bram (1967a, 1967b), Sirivanakarn (1976), Tanaka et al. (1979) and Harbach (1988), but the inclusion of many species in groups and subgroups, especially New World species, is problematic.