['To examine whether treatment with continuous positive airway pressure (CPAP) reduces nocturia in patients with obstructive sleep apnea (OSA).', 'This prospective clinical study recruited patients referred to the Rambam Sleep Laboratory with suspected OSA. After polysomnography, those found to have no OSA were excluded from the study, and the remainder were treated with CPAP. Nocturia was assessed at four time points: baseline (average number of awakenings to urinate per night during 1 week at home before polysomnography); diagnostic night in the laboratory; CPAP titration in the laboratory; and after 1 to 3 months of stable CPAP treatment at home (average number of awakenings to urinate per night for 1 week).', 'Ninety-seven patients (75 men and 22 women) completed the study. The mean +/- SD age was 55 +/- 12 years, body mass index was 33 +/- 7 kg/m2, and respiratory disturbance index was 34 +/- 24/hr. The mean number of awakenings to void at home before CPAP was 2.5 +/- 2.4 times/night; during CPAP, it was 0.7 +/- 0.6 time/night (P < 0.001). A total of 73 patients reported improvement in nocturia. The mean number of awakenings to void in the laboratory was 1.1 +/- 0.9 before CPAP, with a decrease to 0.5 +/- 0.6 during CPAP (P < 0.001). Weak, but significant, correlations were found in the number of awakenings to void before treatment with the respiratory disturbance index (r = 0.25, P = 0.01) and with minimal oxygen saturation (r = -0.23, P = 0.02).'] Does continuous positive airway pressure reduce nocturia in patients with obstructive sleep apnea?