Virological failure of antiretroviral treatment increases the morbidity and mortality associated with AIDS. With currently available drugs it is possible to achieve an HIV - PVL < 50 copies of aRNA/mL in a significant percentage of patients with virological failure, even in those who accumulate a considerable number of resistant mutations in the viral genome. Compliance continues to be the most significant cause of antiretroviral treatment failure. Atazanavir boosted with ritonavir has clear advantages over other protease inhibitors (PI), such as its administration once per day, low number of tablets and a good tolerance which helps in compliance, as well as a lower metabolic toxicity and a resistances profile different to other PIs. Boosted Atazanavir in rescue treatments would be strongly recommended in patients naive to a PI or when there are < 3 mutations in the basic genotype in positions: 10F/I/V, 16E, 33I/F/V, 46I/L, 60E, 84V, 85 V and 90M of the protease gene, particularly when the patient has problems of compliance to antiretroviral treatment or metabolic disorders, such as dyslipaemia, insulin resistance, fasting blood glucose changes, a cardiovascular risk at 10 years of > 10% or cardiovascular disease.