OBJECTIVE: To compare body image perception with body mass index (BMI) calculated from the weight and size declared by subjects, and to evaluate its usefulness in classifying the nutritional status. MATERIAL AND METHODS: A representative sample of the Spanish population was selected consisting of 517 males and 483 females older than 15 years of age. Variables were sex, age, educational level, BMI and perceived body image. Differences between groups were estimated with the chi 2 test. Specificity and sensitivity of the agreement between body mass and image were assessed. RESULTS: The nutritional status for both indicators revealed higher overweight prevalence in males and obesity in females, which increase with age and decrease with greater educational level. Perceived body image differed between sexes, and among ages and educational levels (p < 0.01). Sensitivity and specificity as well as positive and negative predictive values were higher than 0.90 in subjects belonging to extreme cases. Precision was higher for sensitivity than for specificity. In all groups, categorization was better in females than in males and so was Spearman's correlation (p < 0.001). The Kendall W coefficient ranked high for both groups. CONCLUSIONS: Body image allowed the identification of individuals with normal, excessive or lean nutrition. This indicator can therefore be useful in epidemiological surveys, considering some limitations for individualized diagnoses.