The Puerto Rico nightjar is smaller and darker than Caprimulgus vociferus, the species that occurs on the North American mainland. The adult Puerto Rico nightjar is about 21.5 cm long with wings 135 mm long. The throat, upper breast and wing edges are marked with russet. Like all caprimulgids, it has a gaping mouth with conspicuous bristles around the edges. The lateral rectrices show less white than those of Caprimulgus vociferus