Long celebrated for its more than 7,100 islands, the Philippines is a country in Southeast Asia that shares only with Madagascar the distinction of having been designated as both a Megadiverse Nation and a Global Biodiversity Conservation Hotspot. The terrestrial vertebrate fauna of the northeastern Philippines, specifically Luzon Island, has been the subject of intense interest since the first historical explorations. Historically, numerous works considered the biodiversity of Luzon as ?depauperate? in the sense that they was presumed to contain a reduced number of species shared with a continental mainland source. This view has persisted until recently, when a renewed interest in faunistic studies of the northern Philippines has produced a series of notable discoveries, drawing attention to high levels of species diversity and endemism in the northern reaches of the archipelago. We provide the first report on the herpetological biodiversity (amphibians and reptiles) of the northern Sierra Madre Mountain Range, northeast Luzon Island, Philippines. We combine new and historical data, and the results of recent fieldwork, to highlight at least 101 species present in this unique region of the archipelago. Not only is this fauna largely endemic (approximately 70%), but also our results add to a nascent body of literature suggesting that the northern portions of the archipelago may be substantially more diverse than currently appreciated.