Technical Abstract: Hyalopterus is a small genus containing two currently recognized species: Hyalopterus amygdali (Blanchard) and Hyalopterus pruni (Geoffroy). Morpholgical means of distinguishing these species have been difficult and identifications have often been based on host plant data rather than structural characters. Hyalopterus pruni has also been recorded as associated with a number of aphid-transmitted viruses, including plum pox virus, but H. amygdali has not. Both species host alternate between Prunus spp. and Phragmites spp. We present a systematic study of Hyalopterus using a molecular phylogeny derived from mitochondrial, endosymbiont, and nuclear DNA sequences (1,320 bp) and analysis of 16 morphometric characters. The data provides strong evidence for three species (one previously undescribed) within Hyalopterus which confirms previous analyses of host plant usage patterns and suggests the need for revision of this genus.