Quality-of-life (QoL) issues have become increasingly important in health care practice and research. Obstructive sleep apnoea syndrome (OSAS) results in an especially serious reduction in QoL. The purpose of this study was to measure the QoL (life satisfaction) of OSAS patients treated with nasal continuous positive airway pressure (nCPAP). We aimed to determine whether and to what extent the QoL of OSAS patients using nCPAP differs from that of randomly selected subjects without this disorder. The QoL of 67 patients treated for at least 3 months with nCPAP, 21 OSAS patients at the time of OSAS diagnosis, and 113 randomly selected persons visiting the hospital (controls) was investigated with the help of the Munich life-quality dimension list (MLDL), an instrument for cognitive assessment of elementary components (physical condition, psyche, social life, everyday life) of QoL. It was found that QoL of OSAS patients treated with nCPAP did not significantly differ from that of control subjects with regard to elementary components. The 21 untreated OSAS patients showed significantly lower scores in all four subcategories: physical condition (p<0.0005), psyche (p<0.01), social life (p<0.0005) and everyday life (p<0.007). Thus, it may be concluded that nasal continuous positive airway pressure therapy has an important impact on the quality of life of obstructive sleep apnoea syndrome patients, and signifies a further advantage in addition to clinical aspects. Treated patients are as satisfied or dissatisfied with their life as persons without this illness.