In the developed world, Guillain-Barré syndrome and myasthenia gravis account for the majority of cases of acute respiratory failure associated with neuromuscular disease. The 4 components that contribute to respiratory failure are upper-airway dysfunction, inspiratory-muscle weakness, expiratory-muscle weakness, and the pulmonary complications associated with these conditions. Careful observation and objective monitoring are essential to determine the appropriate timing of intubation and mechanical ventilation. Pulmonary function tests that can help predict the need for mechanical ventilation include vital capacity, peak inspiratory pressure, and peak expiratory pressure. The morbidity and mortality of patients who require mechanical ventilation are not insubstantial. This paper will review the mechanisms underlying acute respiratory failure, the clinical assessment of patients, the predictors of the need for mechanical ventilation, and the intensive-care-unit morbidity and mortality of patients with Guillain-Barré syndrome or myasthenia gravis.