Sleep apnea-hypopnea syndrome (SAHS) causes serious symptoms and may induce patients' quality of life impairment. The aim of this study was to assess health related quality of life (HRQOL) in Greek patients with various severity SAHS before and after CPAP implementation in comparison with conservative therapy and Greek population normative data. In 180 patients (152 males, 28 females) with SAHS (apnea-hypopnea index, AHI 56 +/- 25.4/h), daytime sleepiness was assessed with the Epworth sleepiness scale (ESS) and measurements of health status were performed using the short form-36 health survey (SF-36) questionnaire and the General Health Questionnaire (GHQ-30). One hundred and thirty five patients underwent CPAP treatment and 45 were assigned to a conservative therapy. After 3 months the measurements were repeated in 105 patients under CPAP treatment and in 15 patients from the conservative group. HRQOL in all patients was lower than Greek normative data before any treatment. In patients with CPAP therapy the ESS decreased (p<0.01) and a significant improvement was observed in SF-36 dimensions (p<0.01). The improvement was more obvious in patients with severe SAHS (p<0.05) than in patients with moderate disease severity. In the majority of patients (60.9%), GHQ-30 score was high and it was negatively related to some SF-36 dimensions and positively to ESS. In patients under conservative therapy, no significant changes were observed in any measure. HRQOL in patients with SAHS at the time of diagnosis was low and reached general population levels in patients treated with CPAP. The improvement was greater in those with severe syndrome.