The narrow-lined tree frog (Isthmohyla angustilineata) is a species of frogs in the family Hylidae found in the mountains of Costa Rica and western Panama. Its natural habitats are humid lower montane rainforests. It is a nocturnal species that breeds in small puddles and water-filled depressions.
Population declines of this species have been attributed to chytridiomycosis. It is found in several protected areas.