The problem of sibling species in anopheline mosquitoes and the taxonomic approaches applied to their study is evaluated. The existence of sibling species is generally suggested by the observation of puzzling biological or morphological variations, but only rarely do these variations provide definite taxonomic approaches in the study of sibling species of anopheline mosquitoes, and they should be routinely used by the medical entomologist involved in malaria control or eradication projects. The present stage of application of biochemical methods still appears to be of minor importance for the practical recognition of sibling species.