Atelectasis occurred in 17 of 20 patients treated with assisted ventilation for respiratory failure due to neuromuscular disease. A retrospective review of chest roentgenograms and medical records indicated that atelectasis occurs early in the course of respiratory failure and has a predilection for the lower lobes. Atelectasis was associated with infection and persisted despite therapy, often for more than four weeks. This study demonstrates that atelectasis in this condition still occurs frequently despite modern practices of mechanical ventilatory assistance. Infection, occurring soon after intubation, is identified as the principal cofactor.