This study was designed to determine the relationship of dimensions, wall thickness and function of the left ventricle with diabetes duration, fasting blood glucose, lipid profile, beta-OH-butyrate, free fatty acids (FFA) and carnitine levels in children and adolescents with type 1 diabetes mellitus (DM1) who had no cardiovascular complications. Thirty-five patients with DM1. (18 F/17 M, mean age: 12.0 years) and age matched control children (n = 24) were enrolled in the study. Patients with DM1 were subdivided into Group I (mean DM1 duration 3.5 years, n = 14), and Group II (mean DM1 duration 8.2 years, n = 21). Dimensions, wall thickness and systolic functions of the left ventricle were normal in all patients with DM1. Diastolic functions were normal in Group I. In Group II, peak A wave velocity (AVEL) (p = 0.004), velocity-time integral of A wave (AVTI) (p = 0.007) and isovolumetric relaxation time corrected by heart rate (cIVRT) (p = 0.048) were high, and peak E wave velocity (EVEL) and velocity-time integral of E wave (EVTI) were normal. E/A (p < 0.0001) and EVTI/AVTI (p = 0.001) were low in this group. In Group 1, systolic and diastolic blood pressure, HDL-cholesterol and FFA values were normal; total cholesterol (p = 0.047), LDL-cholesterol (p = 0.017), beta-OH-butyrate (p = 0.003), and acetyl carnitine (p = 0.006) levels were high. In Group 11, diastolic blood pressure (p = 0.008), total cholesterol (p < 0.0001) and LDL-cholesterol (p < 0.0001) were increased; and total carnitine (p = 0.019), free carnitine (p = 0.002) and HDL-cholesterol (p = 0.039) were decreased. Correlations were detected between total carnitine and AVEL and HR; free carnitine and AVEL, E/A and HR; HbA(1c) and EVTI/AVTI and cIVRT; LDL-cholesterol and E/A, EVTI/AVTI ratios and cIVRT; HDL-cholesterol and AVEL; FFA and LVDD, IVSD, LVPWD, LVmass and CO; metabolic parameters and DM1 duration and echocardiographic findings such as AVEL, EVEL, EVTI, VmaxAV and CO. In conclusion, left ventricular dimensions, wall thickness and systolic functions were normal in children and adolescents with DM1 who had no obvious cardiovascular complications. Left ventricular diastolic functions were abnormal in patients of Group II. Left ventricular diastolic function abnormalities were associated with glycemic control, free and total carnitine, and LDL- and HDL-cholesterol levels.