We aimed in 186 patients with obstructive sleep apnoea, consecutively treated with nasal CPAP between January 1990 and December 1997, to evaluate compliance with nCPAP therapy and to explore factors influencing compliance. At 3 to 6 months (K1), 1 to 2 years (K2) and more than 3 years (K3) patients were reexamined regarding clinical conditions, the mean time of nCPAP usage per night, nCPAP pressure, and body mass index (BMI). The regularly conducted controls consisted of checking mask fitting, polygraphy with automatic pressure titration and once, mostly at K1, polysomnography. Compliance with nCPAP was considered to be sufficient more than 4 hours of usage per night. At K1, 9 patients had stopped therapy, 5 had moved away, 6 had changed therapy, 6 had died, and 41 had not been treated long enough to have a follow-up at K1. Thus we were able to reexamine 119 patients with ongoing nCPAP therapy. We found no correlation between indices of severeness of sleep apnoea (apnoea/hypopnea index, mean low of night time oxygen saturation, nCPAP pressure, and BMI) and compliance. At K1 87 patients (73%) had sufficient nCPAP compliance. All of them showed sufficient compliance at K2 and K3 too. We conclude that a sufficient compliance at an initial control implies sufficient compliance later on. 32 patients (27%) showed insufficient compliance at K1. Of this group 41% (13 patients) improved compliance at K2. This result underlines the value of a second instruction in nCPAP therapy when patient compliance was lacking initially.