Obesity is a prevalent pathological and nutritional disease relating to clinical and sub-clinical disorders. Furthermore, its complications exert a major impact on cardiovascular risk. Myocardial performance index (MPI) has been described as noninvasive Doppler measures of left ventricular (LV) function. The purpose of this study was to assess MPI using transthoracic Doppler echocardiography in normotensive obese and hypertensive obese pediatric patients and in a control group, and to investigate the relationship between MPI and LV mass, and LV systolic and diastolic functions. The study group consisted of 25 healthy cases (M/F: 13/12) as a control group (Group I), 25 normotensive-obese patients (M/F: 13/12) (Group II) and 25 hypertensive-obese patients (M/F: 14/11) (Group III). The mean ages were 12.1+/-1.8, 11.9+/-1.5 and 12.4+/-1.4 years, respectively. Cholesterol levels and body mass index (BMI) were higher in the hypertensive-obese group. The MPI values were 0.37+/-0.04, 0.43+/-0.08 and 0.51+/-0.11 in the three groups, respectively. MPI measurements, LV mass fractional shortening (FS), ejection fraction (EF) and mitral E/A ratio were found significantly different, especially in the hypertensive-obese group. These findings may be important to determine the relationship between obesity and cardiovascular risk factors in pediatric ages. MPI may be useful in determining the relationship between them.