Two patients who had had acute poliomyelitis with respiratory insufficiency developed respiratory failure 14 and 21 years after the original illnesses. One was a man who had had acute poliomyelitis at age 35; at ages 58 and 59 he was hospitalized five times in respiratory failure in a period of 8 months. The first four of these times he was mechanically ventilated in the hospital and discharged with advice to use low-flow oxygen at home. On the fifth hospitalization mechanical ventilation was effective but deterioration followed weaning. This was resolved by mechanical ventilation during sleep only. The patient was trained to use a pressure-cycled ventilator during sleep at home and has done well for about six years to date. The second patient had had acute poliomyelitis at age 5, had been hospitalized several times in his twenties, and was hospitalized at age 32, comatose. After a long period of mechanical ventilation he was weaned but soon worsened. Nighttime-only ventilatory support was tried successfully. The patient was discharged home to use the ventilator during sleep and to use low-flow oxygen during the day. It is theorized that kyphoscoliosis and respiratory muscle weakness in these patients led to lung compression, increased work of breathing, and progressive alveolar hypoventilation. Because respiratory gas exchange worsens during sleep in the presence of neuromuscular disorders, such patients may require ventilatory support during sleep, with or without supplemental oxygen.