Familial Mediterranean fever is a hereditary disease characterised by recurrent and self-terminated attacks of fever and polyserositis. An earlier study found that adult patients of Familial Mediterranean fever had an abnormally longer QT dispersion and corrected QT dispersion, markers for ventricular arrhythmogenicity. QT dispersion is a simple non-invasive arrhythmogenic marker that can be used to assess homogeneity of cardiac repolarisation; however, it has not been studied in children with Familial Mediterranean fever before. The aim of this study was to assess QT dispersion and corrected QT dispersion, and their relationship with systolic and diastolic function of the left ventricle in a group of children with Familial Mediterranean fever. We performed electrocardiography and Doppler echocardiography on patients and controls. Maximum QT, minimum QT, QT dispersion, corrected QT, maximum corrected QT, minimum corrected QT, and corrected QT dispersion intervals were measured from standard 12-lead electrocardiography. No statistically significant differences were found between the groups in QT dispersion, corrected QT dispersion, and systolic–diastolic function of the left ventricle parameters. During the 12 months of follow-up, no ventricular arrhythmias were documented in either group.