Plectrohyla avia is the largest member of the genus Plectrohyla, with males reaching about 90 mm (3.5 in) and females about 70 mm (2.8 in) snout–vent length. It was described by Laurence Cooper Stuart in 1952 based on a single specimen. This specimen—the holotype—is an adult male that measured 86 mm (3.4 in) SVL. The tympanum is small but very distinct. There is a heavy supratympanic fold that merges with the fold-like canthus (or in less technical terms, "lateral skin folds"). The fingers have vestigial webbing whereas the toes are moderately webbed. The prepollex ("spikethumb") is simple and horny. Vocal slits are absent. The teeth of the upper maxilla are long and protruding.
Based on an observation from Chiapas, breeding takes place underwater and involves axillar amplexus. Male advertisement call is a brief and rapid trill. Males were observed calling underwater and from within small holes and crevices in the splash-zone of waterfalls.
