In 32 patients with the onset of myasthenia gravis after age 50, myasthenic crisis occurred in 53% and persisted for a mean of 33 days (range six to 84 days). Three of the patients had a second crisis. Precipitating factors were found in 60% of the episodes. Treatment of 20 episodes of crisis resulted in excellent recovery. No patient died in crisis. All regained enough function to return home. Those patients (50%) who had no medical complications recovered most rapidly. The most common medical complications were aspiration and bacterial pneumonia, cardiac arrhythmias, and congestive heart failure. Large doses of prednisone in combination with serial plasma exchanges was the most effective therapy. This group of patients had the fewest medical complications (29%) and the fastest recovery.