Sleep-disordered breathing (SDB), especially sleep apnea-hypopnea syndrome, is often observed in patients with type 2 diabetes mellitus; but there are only a few studies on SDB in Japanese diabetic subjects. We investigated the prevalence of SDB in diabetic patients; associations between severity of sleep apnea (SA) and clinical factors, visceral fat, and adiponectin; and associations between type of SA and clinical factors. In the present study, 40 Japanese diabetic patients underwent overnight cardiorespiratory monitoring, and night and morning measurements of serum adiponectin concentrations. Sleep apnea was detected in Japanese diabetic patients at a high prevalence (77.5%). The following variables were associated with SDB: age, body mass index, estimated visceral fat area, and nocturnal reduction in serum adiponectin concentrations. The prevalence of central sleep apnea (CSA, >or=5/h) was 32.3% among diabetic SDB patients. Diabetic SDB patients with CSA had higher hemoglobin, increased intima-media thickness, and higher plasma brain natriuretic peptide levels than those without CSA (<5/h). In conclusion, our study demonstrated a high prevalence of SDB in Japanese diabetic patients, which correlated with visceral fat area and adiponectin. A high frequency of CSA was noted in diabetic SDB patients, together with high hemoglobin, high brain natriuretic peptide, and increased intima-media thickness. The present results of prevalence of SDB may be relevant to the higher incidence of cardiovascular disease in diabetic patients, which need to be clarified in future studies.