BACKGROUND:The aims of this study were to compare compliance to treatment with fixed CPAP and with autoCPAP, subjective preference for type of CPAP treatment, and factors associated to preference for autoCPAP in patients with OSAS. PATIENTS AND METHODS:Twenty-two subjects were studied in a randomized, single blind cross-over fashion. They were treated for one month by fixed CPAP (Elite Sullivan V, ResMed, Sydney, Australia) and one month by autoCPAP (Autoset T, ResMed, Sydney, Australia). RESULTS:Four subjects who stated a preference for fixed CPAP and four who expressed no preference were pooled together; fourteen preferred autoCPAP. Compliance to treatment using the two machines did not differ in the first group (3.8 (1.9) vs. 3.8 (1.5)h/day, fixed vs autoCPAP), but was higher with autoCPAP in the second group (4.8 (1.8) vs 5.5 (1.5)h/day, P<0.05). Baseline apnea/hypopnea index (AHI) was high in both groups, but was higher in the second group P<0.02. First treatment was always fixed CPAP in patients who preferred fixed CPAP, while it was either in the other subjects. CONCLUSIONS:Compliance to autoCPAP differs among OSAS patients. As long as factors predicting higher compliance to autoCPAP are not found, a trial with autoCPAP in patients poorly compliant to fixed CPAP may be warranted.