There are two recognized subspecies, R. s. sulfuratus and R. s. brevicarinatus. R. s. sulfuratus is resident from southern Mexico (Puebla, Oaxaca and Veracruz) south to northern Guatemala and Honduras. R. s. brevicarinatus is resident from southeastern Guatemala and Honduras, through Nicaragua, Costa Rica, and Panama, to northern Colombia (Van Tyne 1929) and northwestern Venezuela (Hilty 2003).
The northern subspecies, R. s. sulfuratus is larger and the bill is longer. The red terminal portion of the bill is more extensive. The yellow in the throat and foreneck is paler. The is no, or very little, red margin bordering the yellow of the throat.
Within the southern subspecies, there is some variation in the color of the yellow throat and breast feathers. In three of 25 skins examined, this yellow is much richer and more orange (Van Tyne 1929).
The Keel-billed Toucan (Ramphastos sulfuratus) is in the family Ramphastidae (toucans, aracaris, toucanets, and mountain-toucans), order Piciformes (woodpeckers and allies). Historically, the numbers of species delineated in this genus ranged from eleven to fifteen. Haffer (1974) recognized seven species and, based on bill morphology and vocalizations, divided these into two groups, the smooth-billed, larger "yelpers" and the channel-keel-billed, smaller "croakers". Current phylogenetic analysis also recognizes seven monophyletic groups (R. brevis Choco Toucan, R. vitellinus Channel-billed Toucan, R.sulfuratus, R. toco Toco Toucan, R. tucanus White-throated Toucan, R. dicolorus Red-breasted Toucan, and R. ambiguus Black-mandibled Toucan), and places the Keel-billed Toucan as sister taxon to a clade composed of R. dicolorus, R. vitellinus and R. brevis (Weckstein 2005, Patané et al. 2009).