Sleep apnea syndrome, a sleep-related breathing disorder (SRBD) of which obstructive sleep apnea syndrome (OSAS) is representative, is often associated with obesity, and therefore patients with SRBD might have a high prevalence of chronic kidney disease (CKD). However, the relationship between obesity and the prevalence of CKD has not yet been investigated in a large cohort of patients with SRBD. The Okinawa Nakamura Clinic Sleep Apnea Syndrome (ONSLEEP) registry contains records for all patients evaluated by full-scale polysomnography (PSG) from September 1990 to the end of 2003 (n=5,651). We studied the total of 4,056 (71.8%) of these patients who had an apnea hypopnea index (AHI) of more than 5 events per hour. The glomerular filtration rate (GFR) was estimated using the abbreviated Modification of Diet in Renal Disease equation in the 1,624 patients for whom serum creatinine data was obtained at the time of the PSG. We defined CKD as a GFR of less than 60 mL/min/1.73 m2. The mean age was 49.9+/-13.5 (mean+/-SD) years; the mean body mass index (BMI) was 28.4+/-5.0 (mean+/-SD) kg/m2. We compared the findings with those from participants in the 1993 general screening registry in Okinawa (n=94,267). From among the total 94,267 screening participants, we selected 7,454 subjects who were age- and sex-matched to the experimental group with SRBD; the ratio of cases to controls was thus approximately 1:4. CKD was detected in 496 (30.5%) patients, with SRBD a higher incidence than that in the screened population (9.1%); the adjusted odds ratio (95% confidence interval) was 4.542 (3.922-5.260, p<0.0001). In contrast to the screened population, the prevalence of CKD decreased as BMI increased (it was 35.7% in SRBD patients with a BMI<25.0 kg/m2, 31.4% in those with a BMI 25.0 to 29.9 kg/m2, and 25.2% in those with a BMI > or =30.0 kg/m2); in the controls the values were 8.1%, 10.5%, and 10.6%, respectively. Taken together, these results suggest that surveillance of CKD is warranted among SRBD patients, particularly those who are not obese.