Mechanical ventilation of the patient with severe asthma or chronic obstructive pulmonary disease (COPD) has unique problems not routinely encountered in the more common critically ill patient without significant airflow obstruction. These problems can lead to ventilator induced morbidity and mortality if not recognized or managed appropriately. In both asthma and COPD, full active management with bronchodilators and adjunctive therapies should be undertaken to avoid or minimize the need for ventilatory assistance. Non-invasive ventilation (NIV) has a well-established role in COPD and is now used more frequently than invasive mechanical ventilation. Regular follow-up should include regular spirometry, a plan for the management of deterioration and the institution of prevention strategies. Prevention, early active medical therapy and NIV remain the best ways to manage severe airflow obstruction. If mechanical ventilation is required, care should be taken to assess and minimize excessive dynamic hyperinflation, its complications, myopathy and lactic acidosis.