Recently discovered at two sites in the extreme southwest Brazilian state of Acre, the local and uncommon White-cheeked Tody-Flycatcher is a very distinctive tyrannid virtually restricted to the southeast Peruvian departments of Madre de Dios and Cuzco, and neighboring areas in northwestern Bolivia. It was not described until the 1950s and then went unseen for almost three decades. Males have a black nape, breast sides and flanks, otherwise whitish underparts and cheeks, a rufous crown, olive-green mantle, and a black tail and wings, while females are broadly similar, but lack black on the flanks and wing coverts, and the cheeks are largely black, although there is an obvious white supercilium. The species is insectivorous and usually forages in pairs, frequently with mixed-species flocks, within the crown of Guadua bamboo thickets, where it can be difficult to observe. The White-cheeked Tody-Flycatcher inhabits humid and transitional forests in the lowlands, but has been recorded to 1050 m.