Bolivia holds one of the world's richest avifaunas, but large areas remain biologically unexplored or unsurveyed. This study carried out the first ornithological inventory of one of the largest of these unexplored areas, the yungas forests of Cordilleras Cocapata and Mosetenes. A total of 339 bird species were recorded including 23 restricted-range, four Near-Threatened, two globally threatened, one new to Bolivia and one that may be new to science. The study extended the known altitudinal ranges of 62 species, 23 by at least 500 m, which represents a substantial increase in our knowledge of species distributions in the yungas, and illustrates how little is known about Bolivia's avifauna. Species characteristic of, or unique to, three Endemic Bird Areas (EBAs) were found. The Cordilleras Cocapata and Mosetenes are a stronghold for yungas endemics and hold large areas of pristine Bolivian and Peruvian Upper and Lower Yungas habitat (EBAs 54 and 55). Human encroachment is starting to threaten the area and priority conservation actions, including designation as a protected area and designation as one of Bolivia's first Important Bird Areas, are recommended.