Treatment of sleep apnea-hypopnea syndrome (SAHS) by fixed continuous positive airway pressure (CPAP) requires an in-laboratory titration procedure to determine the effective pressure level (Peff ). We recently reported that one auto-CPAP machine can be used without titration study allowing Peff determination. The aim of this study was to evaluate the accuracy of an auto CPAP trial at home. A 1- or 2-wk automatic CPAP trial was done at home in 40 patients by estimating the reference pressure (Pref ) to be set and a Pref + 3 cm H(2)O/-4 cm H(2)O pressure interval. Peff was then determined according to the percentage of CPAP time that was spent </= Pref. This Peff value was set on a fixed CPAP machine for two additional weeks and a control sleep study was done. The pressure setting on fixed CPAP had to be increased by 1 +/- 1 cm H(2)O (mean +/- SD) above estimated Pref. Sleep improved with fixed CPAP, with a normalization of the apnea + hypopnea index (AHI) in 38 of 40 and resumption of diurnal hypersomnolence. CPAP compliance remained excellent (CPAP use: 6.1 +/- 1.7 h/ night) after 6.5 +/- 2.8 mo of CPAP treatment. These results indicate that auto-CPAP therapy represents a new useful and accurate way to identify conventional CPAP setting outside hospital and sleep laboratories.