The latest theories suggest that resistance to leptin is the first link of the metabolic changes in obesity. In adults, leptin levels predict the onset of the metabolic syndrome (MS) and its components, and in those with metabolic syndrome the worsening of the MS. The objectives of the study was to determine the leptin levels in overweight children and establish correlation of the leptin with changes in glucidic and lipid metabolism present in child obesity, with metabolic syndrome and the influence of lifestyle on leptinemia. The study was performed on 33 subjects, overweight and obese children aged between 5-16 years. The nutritional status was assessed by BMI and laboratory test needed to diagnose MS according to IDF criteria. Fasting leptin levels were determined. Leptin levels in obese were 82,74 ng/ml, in overweight 48,81ng/ml. No statistical significant correlations were found with glucidic and lipidic metabolism changes or with MS. Negative correlation r=-0,58 were between leptin level and physical activity in boys. Leptinemia positively correlates with the degree of the obesity (BMI) , with the degree of abdominal obesity (WC) and negatively with regular physical activity in boys.