OBJECTIVE Poor compliance with continuous positive airway pressure (CPAP) has been identified as a significant obstacle in the treatment of obstructive sleep apnea. While previous studies have focused on diagnostic screening variables, side effects, health beliefs, and measures of disease severity, investigators have generally ignored sleep parameters assessed during CPAP titration as predictors of compliance. As the titration night represents patients' initial exposure to nocturnal CPAP treatment, we hypothesized that nocturnal polysomnographic (PSG) variables, representing improved sleep at this time, would predict higher subsequent compliance. METHODS Prospective analyses of a sequential case series were undertaken using nocturnal PSG variables during titration as early predictors of CPAP compliance. METHODS Accredited sleep center. METHODS Seventy-one patients with sleep apnea, aged 31-78 years, with a mean respiratory disturbance index of 62.0 +/- 32.2. METHODS N/A. RESULTS Compliance was calculated as mean hours per night of CPAP use over the initial follow-up period (mean 46.9 days). Standard PSG variables and subjective reports of sleep were used as predictive variables in multivariate analyses. Mean objective compliance was 5.04 hours per night +/- 2.59. Consistent with our hypothesis, the best predictor of compliance was change in sleep efficiency (SE) from diagnostic to titration night [F (1,66) = 17.31, p < .000 (r = .48)], indicating that patients whose sleep improved most on the titration night had the highest levels of compliance. This relationship was also significant after controlling for measures of disease severity obtained during the diagnostic testing night. Importantly, individuals whose sleep improved on the CPAP titration night had nightly compliance rates of approximately 2 hours greater than patients whose sleep did not improve during titration. CONCLUSIONS The findings suggest that patients' initial experience with CPAP treatment and, in particular, the degree of improvement in sleep during CPAP titration may be crucial factors in determining their subsequent use of this treatment modality.