The aim of the study was to determine the factors which influence the decision to initiate nCPAP therapy in patients with OSA. 184 patients with OSA were enrolled to the study. They were divided into two groups: group "T" ("treated") which consisted of 112 patients who were being treated with nCPAP and group "R" (resigned") which consisted of 68 patients who refused nCPAP therapy. The main causes of their refusal were: the possibility of surgical treatment, nCPAP intolerance and high costs associated with the purchase of a nCPAP device. The mean age of the patients was comparable in both groups (49.2 +/- 8.7 vs 50.5 +/- 10.6 yrs). Patients from group T had a significantly higher body weight and BMI than the patients from group R (106.6 +/- 2.1 kg vs 94.1 +/- 20.9 kg, p < 0.0001 and 35.0 +/- 6.3 kg/m2 vs 31.1 +/- 6.3 kg/m2, p < 0.00005 respectively). The patient evaluation included physical examination, a questionnaire concerning symptoms related with OSA and OSA assessment by poly-MESAM, polysomnography (PSG) before and with nCPAP trial therapy. RESULTS: the following parameters obtained in the poly-MESAM recording differed significantly (p < 0.001) between group T and group R: RDI (54.6 vs 41.7), HRV index (24 vs 11), SaO2 min (67.0 vs 75% and SaO2 mean (84 vs 88%). Analysis of the baseline PSG did not reveal differences in sleep structure in both groups. We found a significantly higher AHI in group T (63.6 vs 44.9, p < 0.00005). PSG confirmed a significantly lower SaO2 min and SaO2 mean in group T (67.0 vs 75.0%, p < 0.001 and 89.0 vs 92%, p < 0.00002 respectively) and also revealed a significantly longer total sleep time with SaO2 < 90% in this group (183.0 vs 55.0 min, p < 0.0005). We did not find any differences between both study groups in the parameters obtained in PSG with nCPAP trial therapy. CONCLUSIONS: OSA patients who decide to be treated with nCPAP are more obese, have a higher BMI and demonstrate a more severe disease assessed by PSG.