Objectives: This was a prospective controlled study to determine the P-wave duration (Pdu) and P-wave dispersion (Pd) in patients with familial Mediterranean fever (FMF). Methods: The study group consisted of 26 children with uncomplicated FMF and 25 age- and sex-matched healthy controls. We performed electrocardiography (ECG) with Doppler echocardiography on patients and controls. All participants underwent 12-lead electrocardiography under strict standards. Pdu and Pd were computed from a randomly selected beat and from an averaged beat constructed from 12 beats, included in a 10-s ECG. Results: The left ventricle (LV) dimensions, LV ejection fraction (LVEF), and LV fractional shortening (LVFS) values, left atrium dimension, and aortic dimension were in normal range in both groups. There were significant differences between the groups regarding LV-isovolumic relaxation time (IRT), LV-isovolumic contraction time (ICT), right ventricle (RV)-ICT, RV-IRT, and Pd (all p<0.0001). However, highly significant positive correlation was detected between LV-ICT, LV-IRT, RV-ICT, RV-IVT, C-reactive protein (CRP), and Pd (r = 0.505, p<0.0001; r = 0.483, p<0.0001; r = 0.433, p = 0.001; r = 0.421, p = 0.001; r = 0.452, p = 0.001; r = 0.478, p<0.0001, respectively). Conclusions: Uncomplicated FMF children who are continuously treated with colchicine and do not develop amyloidosis have abnormal atrial dispersion and therefore seemingly have an increased electrocardiographic risk of atrial fibrillation. © Japan College of Rheumatology 2012.