Respiratory failure is still an important complication of chronic obstructive pulmonary disease (COPD) and hospitalisation with an acute episode being a poor prognostic marker. However, other comorbid conditions, especially cardiovascular disease, are equally powerful predictors of mortality. The physiological basis of acute respiratory failure in COPD is now clear. Significant ventilation/perfusion mismatching with a relative increase in the physiological dead space leads to hypercapnia and hence acidosis. This is largely the result of a shift to a rapid shallow breathing pattern and a rise in the dead space/tidal volume ratio of each breath. This breathing pattern results from adaptive physiological responses which lessen the risk of respiratory muscle fatigue and minimise breathlessness. Treatment is directed at reducing the mechanical load applied to each breath, correcting specific precipitating factors, e.g. bacterial infection, and maintaining gas exchange. Both bronchodilators and oral corticosteroids can improve spirometric results in exacerbations of COPD and should be routinely offered to patients with respiratory failure. Controlled oxygen is still not always prescribed appropriately and high inspired oxygen concentrations can lead to severe acidosis by either worsening ventilation/perfusion mismatching and/or inducing a degree of hypoventilation. Ventilatory support using noninvasive ventilation has revolutionised the approach to these patients. Acute respiratory failure due to chronic obstructive pulmonary disease remains a common medical emergency that can be effectively managed. More attention should be focused on the prevention of these episodes and identifying the factors which cause early relapse.