An observational, cross-sectional study was conducted in a representative sample of the European Union (7155 men and 8077 women) to calculate the underestimation of body weight as assessed by body image among the overweight and obese population and identify the associated factors to this behavior. Participants were older than 15 years and they were living in the 15 European Union countries. Body mass index (BMI) was grouped into 4 categories using the cutpoints established by the WHO, while perceived body image (PBI) was assessed using a nine-silhouettes drawing. The degree of underestimation between PBI as compared to BMI was identified in overweight and obesity categories of BMI. A multivariable logistic regression model for each gender was used to adjust for potentially confounding variables. Men classified themselves worse than women, being more likely to underestimate their body weight (65.2% of men underestimated their weight vs 32.2% women), regardless of other socioeconomic and attitudinal variables. The greatest degree of underestimation was observed in Mediterranean individuals (68.7% of men and 37.9% of women underestimated their weight). The subjects in the 'maintenance' stage of physical activity tended more often to wrongly select their actual image (71.8% for men and 38.7% for women).