Previous attempts to create national BMI curves for Iranian children and adolescents were limited to local databases. The objective of this study was to build national BMI growth charts for children and adolescents and to report the key percentiles and national cutoff points based on the data obtained from all provinces of Iran. We also aimed to compare our BMI curves to WHO and CDC curves. In each province, about 1000 children and adolescents (6-18 years) were randomly selected from the urban and rural areas by the multistage stratified cluster sampling method. Across the entire country, 240 trained researchers visited the participants' homes. After obtaining consent forms, these researchers gathered the demographic data, accurate anthropometrics, and BMI measurements. In the data screening and data cleaning levels, the outliers were removed. Then the data sets were smoothed using the log-transformation method. After this, they were converted to Z-scores based on normal distribution and then transformed back to the original scale. Finally, these data sets were used to determine each percentile. A total of 22,718 final cleaned data were analyzed, including 10,921 (48.1%) boys and 11,797 (51.9%) girls. The normal BMI curves of Iranian children and adolescents and comparison to the WHO and CDC curves are presented here. This study introduces the new cutoff points for categorizing Iranian children and adolescents as underweight, normal, overweight, or obese, based on a large-scale national survey. The fifth BMI percentiles in Iranian boys and girls were significantly lower compared to WHO and CDC fifth percentile. Also, the 95th percentile curve in our study was significantly lower than the CDC 95th percentile curves in boys and girls.