The purpose of this study was to investigate the differences between normal weight and overweight primary schoolchildren in terms of certain cardiovascular disease (CVD) risk factors and furthermore to identify behavioral correlates significantly affecting their body mass index (BMI). The sample consisted of 198 children with a mean age of 11.5 ± 0.4 years (106 females and 92 males). Data was obtained on children anthropometry, plasma lipids, plasma glucose, dietary intake, cardiorespiratory fitness, and physical activity. Significant gender differences were observed for most of these parameters, with boys being more active and fit but also spending more time on sedentary activities and exhibiting higher intake of energy and fat compared to girls. Using the International Obesity Task Force's (IOTF) BMI cut-off points, the prevalence of overweight and obesity was estimated to be 35.6% and 6.7% among boys and 25.7% and 6.7% among girls, respectively. Overweight and obese children had higher levels of plasma triglycerides (TG) and total cholesterol to HDL-cholesterol (TC/HDL-C) ratio and lower levels of HDL-C and physical fitness compared to their normal-weight peers. Among the behavioral variables tested, only participation in organized sports, cardiorespiratory fitness, and TV watching were significantly correlated with BMI, while energy and fat intake were found to have no significant effect. The current study suggests that even in childhood, overweight and obesity are indicative of an unfavorable lipidemic profile. Among the behavioral parameters known to affect BMI, those found to exert a significant effect were organized physical activities, cardiorespiratory fitness, and TV watching, but not energy or fat intake. Am. J. Hum. Biol. 16:639–647, 2004. © 2004 Wiley-Liss, Inc.