Introduction & Objective: In the year 2000, Gallagher presented a new classification for body mass on the basis of the Percentile of Body Fat (PBF), age, and sex. The World Health Organization defines gold standard for obesity as PBF>25% in men and >35% in women. The primary purpose of the study was to evaluate the accuracy of Gallagher’s classification in detecting overweightness and obesity on the basis of WHO gold standard cutoff points. 

Materials & Methods: In this cross sectional- descriptive study the sample consisted of 20163 adults. Body composition measures were obtained, using the Bioelectrical Impedance Analysis (BIA). The detection of obesity was done by computing sensitivity, specificity, Positive Predictive Power (PPV) and Negative Predictive Power (NPV) for various age and sex groups.

 Results: There were 14270 women and 5893 men, ranging in age from 18 to 85 years, who participated in the study between 2009 and 2014. On the basis of Gallagher’s classification, 2549 (43.2%) men and 2992 (21%) women were obese. The WHO gold standard cutoff points showed that 7126 (49.9%) women and 3208 men (54.4%) met the criteria for being classified as obese. The sensitivity ranged from 53.9% to 100% in males and 38% to 85% in females. The range of specificity among males was from 99.4% to 100% it was 100% among females. The NPV ranged from 29.8% to 100% in males and 14.1% to 84.3% in females.The PPV ranged from 99.8% to 100 in males and it was 100% in females. Among females, the increase in age was associated with decrease in sensitivity and NPV. 

Conclusion: Gallagher’s classification is accurate in detecting overweightness and obesity among males between the ages of 18 and 40 however, it is questionable among females.