To measure neck circumference and waist circumference, to compare it between normal and overweight/obese adolescents, and to validate these with body mass index. This cross-sectional study was conducted in 1800 school-going adolescents. Body mass index, waist circumference and neck circumference were measured. Independent samples t-test and Pearson's correlation were used as tests of significance to analyze quantitative data. Positive correlation of neck circumference and waist circumference with body mass index was observed. The neck circumference and waist circumference in overweight/obese adolescents were significantly higher than adolescents with normal body mass index (P<0.001). Area under curve of waist circumference was more than area under curve of neck circumference. Cut-off values of neck circumference for screening adolescent obesity in boys and girls were 30.75 cm, and 29.75 cm, respectively, and waist circumference cut-off value were 70.75 cm for boys and 69.25 cm for girls at fairly good levels of sensitivity and specificity. Neck circumference and waist circumference may be used in clinical practice and epidemiological studies as an index of overweight/ obesity among school-going adolescents.