In July 2001, a Louisiana State University Museum of Natural Science expedition rediscovered the White-masked Antbird (Pithys castaneus) at a site along the Río Morona in northwestern Departmento Loreto, Peru. Prior to this rediscovery, the species was known only from the type specimen, taken in 1937, and nothing was recorded concerning its natural history. The lack of additional specimens led to speculation that P. castaneus was a hybrid. Here, we present data demonstrating that the White-masked Antbird is a valid species, and we report the first observations of its behavior, habitat, morphology, and voice.