Background and Objectives: Previous adult studies have reported that patients with diabetes mellitus (DM) show ultrastructural and functional myocardial deterioration. The aim of this study is to assess whether cardiac functional deterioration may be detected in pediatric patients with type I DM and whether relative short duration of DM and glycemic under-control influence on cardiac function. Materials and Methods: Forty seven pediatric patients with DM and 38 subjects of control group were enrolled. Glycosylated hemoglobin, DM induced complications, left ventricular function using conventional and unconventional echocardiography including tissue Doppler imaging (TDI) and vector velocity imaging (VVI) were evaluated. Results: The conventional echocardiographic parameters, the findings of pulsed wave TDI at the annular level and regional ventricular function by VVI did not show significant difference between the two groups. In the conventional and non-conventional indexes of systolic and diastolic function, no significant relation was found between DM duration and echocardiographic parameters. Conventional parameter, deceleration time and unconventional parameter, E���/A��� showed significant inverse correlations with HbA1c (p=0.042, p=0.016). Conclusion: Childhood and early adolescence tend to have little insight on their illness of DM, and their diet is hard to control. Alteration of myocardiac function induced by DM may be started earlier than the general opinion, and these changes can be accelerated when glycemic control is poor. We recommend early close observation for cardiac function alteration in diabetic patients in addition to other diabetic complications.