Frostius – known as Frost's toads – is a small genus of true toads consisting of only two species endemic to Brazil. The genus was proposed by David C. Cannatella in 1986 based on an analysis of a species previously classified as Atelopus. Various morphological and life-history information first suggested that it is sister taxon to Atelopus or Atelopus + Osornophryne, but later molecular evidence suggests that it is sister taxon to Oreophrynella. It was named for Darrel Frost in recognition of his work on anuran systematics.