Atrial fibrillation (AF) is the most common arrhythmia observed in hypertropic cardiomyopathy (HCM) and is associated with an acute deterioration. Recently, P wave dispersion (PWD) reflecting inhomogenous atrial conduction has been proposed as being useful for the estimation of paroxysmal AF. In this study, we aimed to define the clinical, echocardiographic and electrocardiographic predictors for AF occurence in patients with HCM. Twenty-seven patients diagnosed with HCM and having a history of documented AF attack were compared with 53 age- and gender-matched patients who had no such history. LA diameter was significantly greater and gradient in the left ventricle outflow tract was lower in patients with AF than those without AF. Maximum P-wave duration (Pmax), PWD and PTF1 values were significantly higher in patients with AF. A Pmax>134.5 ms separated the patients with AF from controls with a sensitivity of 92%, specificity of 89% and a positive predictive value of 80%. APWD value>52.5 ms separated patients from controls with a sensitivity of 96%, a specificity of 91% and a positive predictive accuracy of 84%. An LA diameter>4.2 cm separated patients from controls with a sensitivity of 96% and a specificity of 81%. We concluded that LA diameter and PWD values are the most significant predictors for AF occurence in patients with HCM, and simply by measuring Pmax and PWD values, we could easily identify the patients with high risk, and prescribe the necessary treatment and follow-up protocols for such patients. © 2004 Elsevier Ireland Ltd. All rights reserved.