Daytime complaints like fatigue, sleepiness and cognitive dysfunction in neuromuscular disease can be due to nocturnal hypercapnia and hypoxemia. Daytime respiratory diagnostics does not reflect sleep disordered breathing. Nocturnal pulse oxymetry and capnography were performed in 11 patients (15-75 years old) with different slowly progressive neuromuscular diseases. Only four patients complained of dyspnea. Pulmonary function was abnormal in three patients. Blood gas samples showed a hypoxemia in three patients. Pulse oxymetry results were pathological in six patients. Nine patients presented abnormal capnographies. According to these results either nocturnal oxygen application was initiated or ventilatory parameters were modified. Daytime symptoms and muscular strength improved markedly. Capnography and pulse oxymetry should be performed during the course of neuromuscular disease to detect respiratory insufficiency. Capnography seems to be a more sensitive indicator for respiratory impairment especially when artificial ventilation has been initiated.