Background and Aims Body composition is more important than body weight and body fat is a good guideline used to evaluate health Status better than sole weight. The aim of this study was to compare BIA and BMI to evaluate body weight status in autistic children and adolescents males in Iran.

Methods Eighty-one children and adolescents aged 7–13 years old were selected randomly from 4 autism-specific schools in Tehran in 2011. Body composition of children was measured using BIA.

Results The findings revealed that on the basis of body mass index(BMI), 41.9% of children were normal weight (5^th< BMI< 85 ^th), but 16% were overweight (85^th< BMI< 95 ^th), 27.1% obese (BMI>95 ^th) and 14.8% underweight (BMI< 5 ^th), respectively. Based on percent body fat (PBF), 76.5% of children were normal body fat (5^th< PBF < 85 ^th), 3.7% of children were under the 5th percentile, 12.3% were overweight (85^th< PBF< 95 ^th), and 7.4% were above the 95 percentiles.

Conclusions Although using BMI is simple and easy method for evaluating body weight status, measuring body fat by BIA is another alternative which give better picture of body composition in different health settings.