QT interval dispersion (QT(d)) reflects inhomogeneity of repolarisation. Delayed cardiac repolarisation leading to the prolongation of the QT interval is a well-characterised precursor of arrhythmias. Obstructive sleep apnoea syndrome (OSAS) can cause cardiovascular complications, such as arrhythmias, myocardial infarction, and systemic and pulmonary hypertension. The aim of this study was to assess QT(d) in OSAS patients without hypertension. A total of 49 subjects without hypertension, diabetes mellitus, any cardiac or pulmonary diseases, or any hormonal, hepatic, renal or electrolyte disorders were referred for evaluation of OSAS. An overnight polysomnography and a standard 12-lead ECG were performed in each subject. According to the apnoea-hypopnoea index (AHI), subjects were divided into control subjects (AHI <5, n = 20) and moderate-severe OSAS patients (AHI > or =15, n = 29). QT(d) (defined as the difference between the maximum and minimum QT interval) and QT-corrected interval dispersion (QT(cd)) were calculated using Bazzet's formula. In conclusion, the QT(cd) was significantly higher in OSAS patients (56.1+/-9.3 ms) than in controls (36.3+/-4.5 ms). A strong positive correlation was shown between QT(cd) and AHI. In addition, a significantly positive correlation was shown between QT(cd) and the desaturation index (DI). The AHI and DI were significantly related to QT(cd) as an independent variable using stepwise regression analysis. The QT-corrected interval dispersion is increased in obstructive sleep apnoea syndrome patients without hypertension, and it may reflect obstructive sleep apnoea syndrome severity.