The present study is based on material preserved in museum collections, as well as specimens obtained in the course of faunistic work conducted in recent years, and includes all cossid taxa recorded from southwestern Africa thus far. A total of 47 species representing 13 genera are treated. For each genus a differential diagnosis is provided. The following taxonomic changes are proposed: Lichtensteiniana punctulata (Walker, 1856) stat. nov., comb. nov.; Coryphodema coelebs (Clench, 1959), syn. nov. of C. seineri (Grünberg, 1910); Brachylia eberti Yakovlev, 2011 syn. nov. of B. eutelia Clench, 1959; Aethalopteryx forsteri (Clench, 1959), syn. nov. of A. tristis (Gaede, 1915), and Aethalopteryx simplex (Aurivillius, 1905) comb. nov. (from Azygophleps). The species of Rethona Walker, 1855 are revised and illustrations of the adults are provided. Ten new species are described: Lichtensteiniana maritima spec. nov., L. orania spec. nov., Brachylia camparia spec. nov., B. contusa spec. nov., B. minor spec. nov., B. lineata spec. nov., B. fusca spec.nov., B. plumbata spec. nov., Meyoarabiella karooensisspec. nov., and Azygophleps asylasiformis spec. nov. The original description of Phalaena asylas Cramer, 1779 was rechecked. The correct interpretation of this species is still pending. The genitalia of the new species and the adult moths are illustrated. A checklist of all species recorded from the sub-region and a key to all genera occurring in southern Africa are provided.

Keywords: Afrotropical Region, Biogeography, Biology, Botswana, Cossidae, Faunistics, Lepidoptera, Namibia, New Species, New Synonymies, South Africa, Taxonomy.