Introduction: Chile is among the countries with the highest rate of excess malnutrition, for that reason it is important to have effective tools to evaluate the nutritional status; interest in neck circumference (NC) measurement as a potential prognostic tool that is easy to access and low-cost has increased. Objective: to evaluate the diagnostic capacity of neck circumference to predict obesity in the population aged 15-16 years, using data from the third National Health Survey 2009-2010. Materials and methods: Concurrent Criteria of Diagnostic Validation were used for the study. The sample consisted of 536 people of ages from 15 to 26 years, where BMI data where taken in order to classify obesity versus normality (gold standard), as was NC (measured in centimeters). People with hyperthyroidism were excluded. Indicators of diagnostic accuracy were obtained; the SPSS, version 25 was used for calculations. Results: according to age and gender ranks, the NC cut-off points to classify general obesity showed sensitivities and specificities above 0.85, with an area under the curve over 0.90, all with p < 0.001. Conclusion: there is evidence that supports that NC cutoff points are a suitable tool for diagnosing obesity in this age group.