Despite the Gray-cheeked Nunlet having a relatively tiny range, which extends from central Panama as far south as north-central Colombia, three subspecies are generally recognized, and one of these, the nominate, has even been suggested to constitute more than one taxon based on differences in coloration observed in specimens. This species forms a superspecies with the Rufous-capped Nunlet (Nonnula ruficapilla) of southern Amazonia, and the Chestnut-headed Nunlet (Nonnula amaurocephala), which is restricted to a tiny area of northwest Brazil. The Gray-cheeked Nunlet is undoubtedly rare, but the species is not treated as being globally threatened, and its apparent scarcity is assuredly much influenced by the species’ unobtrusive habits and a relative lack of knowledge of its vocalizations. It is usually found at lower levels in moist forests, including riverine patches, second growth and thickets, and has been recorded to at least 1000 m. This nunlet occasionally joins mixed-species foraging flocks, and has been observed taking a variety of insect prey. The nesting behaviour of the entire genus Nonnula is very poorly known, and to date a nest of the Gray-cheeked Nunlet remains to be discovered.