Atopophrynus syntomopus, the Sonson frog, is a species of frog in the Craugastoridae family, of the monotypic genus Atopophrynus. It is endemic to Colombia and only known from its type locality in the Cordillera Central, from Sonsón, Antioquia. The species is known from three specimens recorded on wet rocks very close to a stream in primary forest. It has not been seen in later surveys, and the habitat is degraded by guerrilla activities; it may already be extinct.