Background: Body mass index (BMI) is a growth assessment parameter that is important for nutritional assessment. The secondary school student population is at risk for nutritional disorders due to their growth and developmental needs.

Materials and Methods: A descriptive cross-sectional survey of the quantitative design was conducted in 2021 in Orhuwhorun a town where the Delta Steel Company is located. It is in the Northeast part of the Udu Local Government Area of Delta State, South-South Nigeria. The study population was 420 subjects (210 males and 210 females) secondary school students, 11-16 years old. Statistical Package for Social Sciences (SPSS) version 23.0 was used to analyze the data. The t test was used to determine the statistical mean difference between males and females and between paired samples.

Results: BMI for females was 18.52±4.03 Kg/m2, at 11 years, approximately 21.00 Kg/m2, at 12-14 years and approximately 22.00 Kg/m2 at 15 and 16 years. For males, the mean BMI was approximately 18.00 Kg/m2 at 11 and 12 years, approximately 19.00 Kg/m2 at 13 and 14 years, and approximately 21.00 Kg/m2, at 15 and 16 years. Prevalence of 73.1% of the sample were 5th to 85th percentile; 5.7% were less than 5th percentile; 13.1% were 85th to less than 95th percentile; and 8.1% were 95th percentile and above.

Conclusion: In males, 7.1% was underweight, 73.8% was normal weight, 14.3% overweight and 4.8% obese. In female 4.3% was underweight, 72.4% normal weight, 11.9% overweight and 11.4% obese.

Keywords: Body mass index, obesity, overweight, secondary school students