Genetic variation was assessed for the closely related aphids Myzus nicotianae Blackman and Myzus persicae (Sulzer), previously classified as a single species. Populations of both red and green color morphs, collected from tobacco and nontobacco hosts from 3 continents, were analyzed via random amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR) and mitochondrial cytochrome oxidase II (COII) and elongation factor- 1 alpha (EF-1α) gene sequencing. Three other Myzus species—M. cerasi (F.), M. hemerocallis Takahashi, and M. varians Davidson)—were used as outgroups in our analyses. RAPD-PCR analysis revealed many, easily detectable genetic polymorphisms between the Myzus persicae complex and the outgroup species. The small number of polymorphisms detected within the complex were not correlated with host plant or the geographic origin of populations. The sequences of both COII and EF-1α for all populations within the M. persicae complex were identical, although significant variation was evident between the M. persicae complex and outgroup taxa. These results strongly suggest the synonymy of M. persicae and M. nicotianae.