All individuals in a Swedish county afflicted with any type of hereditary muscular dystrophy (MD) were identified and 57 (85 percent) of eligible individuals in the age range 16 to 64 were included in the study. Respiratory disturbances were estimated by means of spirometry and analysis of arterial blood gases, and 58 percent yielded abnormal results on at least one of these examinations. Elevated PCO2 was found more commonly than reduced forced vital capacity (FVC) and there was a moderate association between these parameters. Respiratory symptoms, most commonly breathlessness, were encountered in 79 percent. Pathologic ECG recordings were found in 21 individuals (37 percent). Conduction disturbances and affection of the myocard were most frequent in myotonic dystrophy. Quality of life was assessed by means of the Sickness Impact Profile instrument and the Kaasa test. The results showed that quality of life was significantly related to FVC and to the symptom of abnormal fatigue. Respiratory and cardiac parameters showed a greater number of significant correlations with measures of functional ability than with subjective well-being.