The Simulium gombakense species-group, one of the 15 species-groups of the subgenus Gomphostilbia Enderlein, is small, being represented by only 12 species, all of which are distributed in the Oriental Region. It is characterized by the pupal gill composed of an inflated structure and eight or ten slender filaments. Among the 12 species, S. sachini Takaoka & Henry, and S. williei Takaoka & Thapa were originally described from two pupae, and one pupa and two larvae, respectively, from Darjeeling, India. In the present paper, the adult females and males of these species are described for the first time from specimens reared from pupae collected at the type locality. Simulium sachini is distinctive in the female by the claw with a medium-sized basal tooth, and in the male by the somewhat enlarged, spindleshaped hind basitarsus and ventral plate with its ventral margin much depressed medially, while S. williei is characterized by the small number of male upper-eye (large) facets in 12 vertical columns and 13 or 14 horizontal rows and ventral plate much produced posteroventrally. Taxonomic notes are given to separate these two species in the adult stage from their related species.