The genus Diastoleus Solier (Tenebrioninae: Scotobiini) is composed of four species restricted to north-central Chile. Representatives of this genus are adapted to inhabit xeric environments. In this paper the genus is revised using external features, new genitalic characters, and internal morphology. A new species, D. costalenissp. nov., is described from Paposo, Antofagasta, northwestern Chile. Habitat records, distribution map, habitus photographs, drawings of metendosternites and aedeagi are included. A cladistic analysis was conducted to test the monophyly of the genus within the tribe Scotobiini.