Acute respiratory failure of chronic obstructive pulmonary disease is a common event. Vital prognosis is seldom directly engaged, and careful management generally allows patients to resume their prior respiratory status, and long term therapeutic procedures such as oxygen therapy or home ventilation to be discussed. Diagnosis is often simple, and evaluation of severity, therapeutic strategy, and etiology research are carried out simultaneously. The first step of treatment is controlled oxygen therapy. When conservative treatment fails to achieve safe level of PaO2 without inducing threatening hypercapnia, mechanical ventilation is required. Recent data strongly suggest that non invasive inspiratory pressure support brings major benefits in terms of morbidity and mortality.