Childhood obesity is nowadays a concern in the developing world. This cross-sectional study was conducted on 501 randomly selected students from 10 high schools in an urban setting in Hyderabad, Pakistan. Children who were underweight were excluded. Interviews were conducted to determine demographic data, dietary intake, physical activity and other variables that may be associated with obesity. Overall 58 students (12%) had body mass index (BMI) ≥ 95th percentile, 40 (8%) BMI ≥ 85th percentile and 403 (80%) had BMI < 85th percentile (WHO age- and sex-specific cut-offs). The prevalence of obesity was higher in boys than girls (15% than 8% respectively). In multivariate regression analysis significant risk factors for obesity/overweight were male sex, middle socioeconomic status, poor self-rated athletic ability, trying to lose weight and eating fruit < 4 times per week. Childhood obesity is determined by factors in the home, school and society and a multidisciplinary approach is needed to prevention.