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Introduction: Obesity is a public health problem that affects and has increased rapidly in the last decade in a large number of countries in the world. Moreover, it is an important cardiovascular risk factor and has been shown to be a possible risk factor in mortality, specially due to chronic disease. Objective: To determine the prevalence of obesity according to three anthropometric indexes: Body Mass Index (BMI), waist circumference (WC) and body fat percentage (%BF) measured by bioelectrical impedance and to estimate the validity and accuracy of BMI and WC indexes to define obesity using %BF as reference method. Material and Methods: We carried out a cross-sectional study that included 141 participants from the Nutrition Survey of Valencian Community conducted in 1994, who were evaluated again 10 years later. Anthropometric measurements were made with standardized protocols for weight and height obtaining BMI, WC and % BF. We classified the participants as obese (yes/no) using the following cut-off points of BMI >= 30kg/m(2), WC>102cm in men and >88cm in women, and % BF >27 for men and 40 in women. Correlation coefficients between anthropometric indexes adjusting by age were obtained. Sensitivity, specificity and predictive values were estimated for BMI and WC using % BF as reference. Results: The prevalence of obesity was 19.9%, 37.6 and 38.3% using BMI, WC and % BF respectively. The correlation coefficients ranged from 0.232 for WC-% BF and 0.829 for BMI-WC. Using the % BF as reference, the BMI showed greater specificity (92.6% in women and 93.9% in men) and WC greater sensitivity (83.3% in women and 53.7% in men) to detect obesity. Conclusions: The prevalence of obesity differs according to the anthropometric index used. WC, given its easy measurement may be the most appropriate indicator to be used in population-based studies and preventive programs to detect obesity in adults.