The brown-billed scythebill (Campylorhamphus pusillus) is a species of bird in the subfamily Dendrocolaptinae of the ovenbird family Furnariidae.

Adults of the nominate subspecies have a face and neck streaked buff and blackish brown, with a faint buffy supercilium.

Their crown and nape are dark brown, with thin deep buff streaks that extend sparsely onto the upper back.

Their underparts are dark brown to olive-brown that becomes more rufescent on the lower belly and undertail coverts.

[4][5][6][7] The brown-billed scythebill is believed to be a year-round resident throughout its range, though some elevational movements are suspected in Central America.

It typically takes its prey from the surface of the substrate, and also by probing crevices and holes in bark, bromeliads, epiphytes, moss, and vine tangles.

Its song is complex and highly variable, a "series of notes lasting 2·5–5 seconds, beginning with a soft, twittering trill that continues in background during a series of loud whistles that are usually descending (sometimes ascending) and somewhat quavering, e.g. 'wheéwhipwhipwhipaweé, at-t-t-t-t-weeaweéaweé' or 'twe-weo-WEO-weo weo-we-we-we-we-we' ".

It is "[b]elieved to be highly sensitive to human disturbance, requiring extensive tracts of unbroken forest [and] locally at risk in Chocó of SW Colombia, where it is limited by lack of habitat.