Two subspecies are recognized:
serus Friedmann 1950; type locality Río Indio, Canal Zone, Panama
Occupies the greater part of the distribution of the species, from Mexico south to Bolivia and central Brazil.
Similar to tyrannus, but averages smaller (see Measurements); "under wing coverts less heavily marked with black; flanks and tibiae more heavily marked with white crossbars" (Blake 1977).
tyrannus (Wied 1820); type locality Rio Belmonte, Bahia, Brazil.
Occurs in eastern Brazil, from Bahia south, and in northeastern Argentina.
Averages larger in size than serus (see Measurements); "under wing coverts more heavily marked; flanks and legs more extensively black, with narrower wihite barring" (Blake 1977).
Two independent phylogenetic analyses of DNA sequence data (from both mitochondrial and nuclear genes) reached similar conclusions regarding the relationships of Spizaetus (Helbig et al. 2005, Lerner and Mindell 2005). Spizaetus ornatus (Ornate Hawk-Eagle) and Spizaetus isidori (Black-and-chestnut Eagle) constitute sister species, and Spizastur melanoleucus (Black-and-white Hawk-Eagle) is sister to this clade, with tyrannus at the base of the Spizaetus clade (Helbig et al. 2005, Lerner and Mindell 2005). These studies also confirmed that the New World clade is not the sister group of the Old World species formerly also classified in the genus Spizaetus, a conclusion that previous morphological studies first had suggested (Jollie 1976-1977).