Nocturnal hemodialysis has been shown to improve sleep apnea in patients who receive conventional hemodialysis. It was hypothesized that nocturnal peritoneal dialysis (NPD) also is effective in correcting sleep apnea in patients who receive continuous ambulatory PD (CAPD). Overnight polysomnography (PSG) was performed in 46 stable NPD and CAPD patients who were matched for demographic and clinical attributes. The prevalence of sleep apnea, defined as an apnea-hypopnea index (AHI; or frequency of apnea and hypopnea per hour of sleep) >15, was 52% for NPD patients and 91% for CAPD patients (P ‫؍‬ 0.007). The mean (؎SD) AHI in NPD and CAPD patients was 31.6 ؎ 25.6 and 50.9 ؎ 26.4 (P ‫؍‬ 0.025), respectively. For validation of the efficacy of NPD in alleviating sleep apnea, a fixed sequence intervention study was performed in which 24 incident PD patients underwent one PSG study during mandatory cycler-assisted NPD while awaiting their turn for CAPD training and a second PSG recording shortly after they were established on stable CAPD. The prevalence of sleep apnea was 4.2% during NPD and 33.3% during CAPD (P ‫؍‬ 0.016). AHI increased from 3.4 ؎ 1.34 during NPD to 14.0 ؎ 3.46 during CAPD (P < 0.001). With the use of bioelectrical impedance analysis, total body water content was significantly lower during stable NPD than CAPD (32.8 ؎ 7.37 versus 35.1 ؎ 7.35 L; P ‫؍‬ 0.004). NPD delivered greater reductions in total body water (؊2.81 ؎ 0.45 versus ؊1.34 ؎ 0.3 L; P ‫؍‬ 0.015) and hydration fraction (؊3.63 ؎ 0.64 versus ؊0.71 ؎ 0.52%; P ‫؍‬ 0.005) during sleep. Pulmonary function tests remained unchanged before and after conversion from NPD to CAPD. These findings suggest that NPD may have a therapeutic edge over CAPD in sleep apnea that is associated with renal failure as a result of better fluid clearance during sleep.