Three subspecies of the Mottle-cheeked Tyrannulet are recognized over the species’ wide range, in the east Andes from northern Peru to northwest Argentina, and in the Atlantic Forest region, from southeast Brazil to northeast Argentina, including parts of Uruguay and eastern Paraguay. Its plumage is typical of the genus, being principally olive-green above and paler below, with obvious wingbars and prominent white markings on the tertials, and the species’ behavior also is ‘normal’, as it perches broadly horizontally and holds the tail at most slightly cocked. Mottle-cheeked Tyrannulet also regularly joins mixed-species flocks and forages very actively, apparently exclusively for invertebrates. The species’ overall altitudinal range encompasses 1000–2200 m, within which it inhabits a range of forest habitats. Given the Mottle-cheeked Tyrannulet’s relative abundance, it is unsurprising that most aspects of the species’ biology and behavior are relatively better known than for many other congeners.