OBJECTIVE It was hypothesized that sleep disorders might be present due to functional heart failure in patients with mitral stenosis (MS), and might be accompanied by obstructive-type sleep disorders. To examine this hypothesis, non-smoker and non-obese patients with rheumatic MS and without concomitant diseases were investigated for sleep disorders. METHODS Patients admitted to the cardiology outpatient clinic at the authors' institution for rheumatic MS during a one-year period were included in the study. Patients were evaluated using the Epworth sleepiness scale, apnea-hypopnea index (AHI), and echocardiographic examination. The relationship between echocardiographic findings and AHI was assessed. RESULTS Eighteen patients were included in the study. All patients had sinus rhythm and normal electrocardiography recordings, with no coronary artery disease or concomitant cardiac disease. Obstructive sleep apnea (OSA) was determined in 16 patients. AHI was positively correlated with the mean apnea duration, mean gradient, rapid eye movement (REM)-AHI and non-REM-AHI. AHI, pulmonary artery pressure, mitral valve area, mean gradient, left ventricular end-systolic diameter, left ventricular end-diastolic diameter and mean REM-AHI differed significantly according to the degree of MS. AHI was shown to be increased as the degree of MS increased. CONCLUSIONS The frequency of OSA was found to be significantly higher in patients with MS. In addition to cardiac problems, these patients need to be evaluated also for sleep problems and treated appropriately.