Background: Atrial fibrillation (AF) is a frequent arrhythmia, associated with morbidity and mortality. It is identified by two types on surface electrocardiogram as fine and coarse AF. We aimed to search the association of subtypes of AF with clinical parameters. Methods: Eight hundred and eleven consecutive patients, who had AF attack which lasted longer than 24 h or more, were evaluated along with clinical and laboratory data. Results: Coarse AF was noticed in 51.7% (n = 419), and fine AF in 48.3% (n = 392). Sex was associated with subtype of AF such that coarse AF was present in 46.5% of male patients, but in 56.1% of female patients (p = 0.009). Coarse AF was present in 85.3% of patients with mitral stenosis, whereas it was present in 35.3% of patients with normal heart valve (p < 0.001).). Patients having fine AF were significantly older than those having coarse AF (64 +/- 12, 57 +/- 13 years, p < 0.001). 19.6% of those with coarse AF had history of cerebrovascular event (CVE), whereas 13.5% of those with fine AF had history of CVE (p = 0.021). After controlling for age in the multivariable logistic regression analysis, presence of coarse AF (B = 1.585, p = 0.031) was found to be independently associated with the history of CVE. Conclusion: AF is identified by two morphological forms on the surface electrocardiogram. These two forms were found to be associated with different clinical parameters, acting on vascular endpoints differently. Copyright (c) 2007 S. Karger AG, Basel.