We evaluated a 2-year experience involving 22 patients who required prolonged mechanical ventilation for respiratory failure associated with myasthenia gravis. The most frequent cause of respiratory failure was operation, and the most common type of procedure was thymectomy. Next in frequency as exacerbating factors were myasthenic crisis and cholinergic crisis. Of the 22 patients, 21 survived and were weaned from the ventilator after 1 to 32 days of respiratory support.