Approximately 25 % of all patients suffering from obstructive sleep apnea syndrome (OSAS) discontinue CPAP-therapy in long-term follow-up. This study was conducted to investigate if there are any predictors signaling low compliance prior to initiation of CPAP-therapy. We used an open label longitudinal cohort study at an University hospital in-patient Sleep laboratory setting. In 85 consecutive patients with a diagnosis of OSAS confirmed by polysomnography a CPAP-therapy was initiated. Prior to CPAP-titration the subjects were interviewed using standardized, validated questionnaires (Nottingham Health Profile, von Zerssen's Depression Scale, State Trait Anxiety Inventory, IPC-Scale). On follow up (mean 16 +/- 8 month) 66 patients were still using CPAP regularly, 19 individuals had discontinued the therapy. Data of both groups were compared. There were no significant differences in polysomnographic parameters before CPAP except apnea-hypopnea-index (users: 30.72 +/- 20.68, rejecters: 18.43 +/- 10.43) and mean oxygen saturation (users: 91.65 +/- 3.32, rejecters 93.63 +/- 1.86). Depression and anxiety levels were normal in both groups. The subjects who discontinued CPAP had a significantly less external control belief. Internal control belief was normal in all patients. It is suggested that individuals who discontinued CPAP could not be convinced of the necessity of CPAP by physicians or nurses due to their reduced external control belief. Identifying patients with diminished external control belief prior to prescription of a device might be useful. In selected subgroups, different methods of motivation to maintain long-term acceptance for CPAP-therapy seems to be necessary.