The aim of the study was to estimate the prevalence of prolonged corrected QT interval and increased QT interval dispersion among patients with hypertrophic cardiomyopathy (HCM) and their association with clinical and instrumental data and risk factors of sudden death. Ninety patients with HCM were observed. Patients with HCM and long corrected QT interval on standard ECG at rest have risk factors for sudden cardiac death in 75.8 % cases. Arrhythmias, such as premature ventricular complexes and unstable ventricular tachycardia, occur significantly more often in patients with long corrected QT interval. Positive correlation was detected between corrected QT interval, QT dispersion and risk factors of sudden cardiac death, such as unstable ventricular tachycardia, hypotension at physical activity, atrial fibrillation, outflow tract obstruction and left ventricular wall thickness 3 cm or more. Strong positive relationship was revealed between QT dispersion and restrictive type of diastolic dysfunction, which develops at later stages of the disease and is associated with fibrotic changes of myocardium.