BACKGROUND:The duration of automatic computer-controlled continuous positive airway pressure device (autoCPAP) initiation at home varies largely between sleep centers. Our objectives were to evaluate the cost-effectiveness and to find the optimal trial duration. METHODS:Of the 206 consecutive CPAP-naive patients with obstructive sleep apnea syndrome, who were referred to our hospital, 166 received autoCPAP for a 5-day trial at home. RESULTS:Of the 166 patients, 89 (15 women) showed a successful 5-day autoCPAP trial (normalized oximetry and mask-on time exceeding 4 h/day for at least 4 days). For the first trial day, 88 (53%) patients had normalized oximetry and a mask-on time exceeding 4 h. A 1-day autoCPAP trial EUR 668 was less cost-effective than a 5-day trial EUR 653, with no differences in values of efficient CPAP pressure or residual apnea-hypopnea index (AHI). The systematic requirement of oximetry monitoring raised the cost considerably from EUR 481 to EUR 668. CONCLUSIONS:In selected patients with obstructive sleep apnea, the optimal duration for initiating CPAP therapy at home by autoCPAP is 5 days. Although a 1-day trial was sufficient to determine the CPAP pressure requirement, it was not cost-effective and had a high rate of failure.