Overweight and obesity in children are a serious problem. They are increasingly prevalent and associated with a wide range of health problems in adulthood. Monitoring their status is essential for effective planning in the health system.. This study aimed to assess the prevalence of overweight and obesity in children below 5 years in Tehran in 2012.Patients and This cross-sectional study employed data provided by the urban health equity assessment in Tehran. The sample comprised a total of 4656 children under 5 years, recruited via multistage sampling. Data were collected through questionnaires and anthropometric measures of height and weight. The WHO child growth standards were used to determine overweight and obesity. Data were analyzed using chi-square tests, with SPSS version 11.5. The prevalence of overweight and obesity in children were 12% and 23.7% respectively. The prevalence of overweight was significantly higher in girls than boys and the prevalence of obesity was significantly higher in boys than girls (P = 0.001). Obesity was more prevalent in children from high economic percentiles, but this finding was not statistically significant. The prevalence of overweight and obesity in children under 5 years is high. Overweight and obesity should be considered an epidemic and serious health problem in Tehran. They certainly require more attention and intervention.