Background: Dental caries is the single most common disease in children that has no pharmacological treatment. Global population exhibit some evidence of tooth decay affecting both genders, all races, socioeconomic status and age groups. Good oral health of early childhood has a vital role in overall health of school children. Objectives: The aim of this study was to determine association of weight, height, and body mass index (BMI) with early childhood caries (ECC) among primary school children of Peshawar. Study Design: Cross sectional study. Setting: Different Schools of Hayatabad, Peshawar. Period: Four months (January-April 2019). Material and Methods: Total of 240 school children, having sound heath with no systemic disease were included in the study. Children’s weight and height were recorded and body mass index (BMI) was converted to z-scores and percentiles. The association of ECC with BMI, height and weight was determined. Results: The mean age, weight, height, body mass index, dmfs and Z-score was 5.3±0.79 years, 20.34±3.75 kg, 3.47±0.246 feet, 18.06±4.08 kg/m2, 14.84±15.73, and 1.14±1.22 respectively. The association of early childhood caries among primary school children was not significant with age (P=0.424), height (P=0.622) and gender (P=0.061). The association was highly statistically significant with BMI (P<0.001). Conclusion: Children with higher ECC scores were significantly associated with BMI.