In the midst of the effervescent discussions of climate change and setbacks in national environmental protection mechanisms, the Brazilian Amazon and its ichthyofauna are in the spotlight. Therefore, in this work we redescribe Hypostomus carinatus (Steindachner 1881), a little known medium-sized Amazonian species, providing means for its correct identification and taxonomic stabilization. In this way, based on the analysis of type specimens and recently collected material, H. carinatus is redescribed and its geographical distribution is expanded to the basins of the Branco, Japurá, Juruá, Solimões, Negro, Tapajós, Trombetas and Uatumã rivers. A lectotype of the Plecostomus carinatus is designated herein. Hypostomus carinatus is mainly distinguished from congeners by the presence of four to ten predorsal plates posteriorly surrounding parieto-supraoccipital bone; dark spots on body and fins; by having the dark spots smaller or almost equal to distance among each spot; body carenae armored with odontodes; and compressed head with eyes laterally positioned.