The salivary gland chromosomes of Anopheles (Stethomyia) kompi, the firs described from this subgenus, differ clearly from chromosomes of the subgenera Anopheles, Cellia and Nyssorhynchus. A population from Manaus, Brazil contains three paracentric inversions, apparently in Hardy-Weinberg equilibrium. A closely related species, An. nimbus occurs in the same larval habitat. The 2 species cannot be reliably distinguished morphologically but are clearly separable cytologically. There is no evidence of hybridization in this population.