To assess right- and left-ventricular function in children with type 1 diabetes mellitus (DM) as well as correlate cardiac function with diabetes duration and state of metabolic control. The present study included 30 patients with type 1 DM (group 1) and 20 apparently normal children with comparable age and sex as controls (group 2). All children were subjected to detailed history, clinical examination, and routine laboratory investigations, including glycated hemoglobin, as well as conventional echocardiographic and tissue Doppler examination. Children with type 1 DM have impaired diastolic function in both left and right ventricles before the development of systolic dysfunction when assessed with either conventional or tissue Doppler echocardiography. Resting heart rate in diabetic patients showed a significant positive correlation with mitral A flow velocity and a significant negative correlation with mitral and tricuspid E/A ratio. Regarding morphological parameters of the left ventricle, all dimensions and volumes were comparable between diabetic patients and controls; however, a significant positive correlation was found between interventricular septal thickness at diastole (IVSd), interventricular septal thickness at systole (IVSs), and left ventricular posterior wall at systole (LVPWs) and the duration of diabetes. Children with type 1 DM have impaired diastolic function in both left and right ventricles with normal systolic function when assessed with either conventional or tissue Doppler echocardiography.