Few data exist regarding the resistance profile in individuals receiving atazanavir. We found that ritonavir-boosted atazanavir is not associated with the development of primary genotypic resistance in individuals failing this combination, without previous protease inhibitor failure. It is rarely associated with the acquisition of primary mutations in individuals with previous protease inhibitor exposure. This is particularly important because of the increasing use of atazanavir monotherapy, and implies that treatment failure is caused by lack of potency.