The diversity of the grass flora (Poaceae) of the Region of Aysén, Chilean Patagonia (43º38’-49º16`S), was studied in order to develop a checklist of the species, to evaluate the completeness of the inventory, and to determine the distribution of the collected specimens and species richness facilitating new expeditions. In Aysén, Poaceae are represented by 36 genera, 122 species and 12 infraspecific taxa, distributed in 3 subfamilies: Bambusoideae, Danthonioideae and Pooideae. Species accumulation curves and the Chao 2 index suggested that it would still be possible to detect between 113 and 32, with an average of 60 new species. These values suggest that the inventory is completed between 52 and 80%. The species richness is directly related to the collection effort; the greatest number of species were found in Coyhaique and General Carrera. It was shown that most of the collections were concentrated in the vicinity of roads and cities, in three areas of the region: Puerto Cisnes-La Tapera, Coyhaique, and near Chile Chico (National Reserve Lago General Carrera, N. R. Jeinimeni). Other collected zones include the protected areas National Reserve Trapananda, National Park Queulat, N. P. Laguna San Rafael, N. P. Isla Magdalena, N. P. Cerro Castillo, and N. R. Lago Las Torres.