Abrothrix lanosus, distributed throughout southern South America, is one of the least known Patagonian sigmodontine rodents. So far, neither a topotype from the type locality, the Madre de Dios Archipelago (Chile), neither specimens from adjacent areas have been collected. In this contribution, seven new recording localities and a topotype are given. The measurements of gross morphological features, including the cranium of the first topotype collected and other seven individuals are reported. Moreover, the findings establish new northern (48°11’ S, 74°25’ W) and western (49°25’ S, 75°27’ W) distribution limits in Chile for the species.