Underweight, overweight and obesity are associated with increased mortality from several chronic diseases, including cancer. Self body weight misperceptions affect weight control. We monitored weight perception in Italy on a total of 14 135 individuals (6834 men, 7301 women), representative of the Italian adult population with available information on body mass index (BMI) derived by self-reported height and weight. Differences in misperception of BMI categories across subpopulations were analysed using unconditional multiple logistic regression models after adjustment for a number of covariates. Overall, 66.4% of individuals accurately perceived, 21.0% underestimated and 12.6% overestimated their category of BMI. In men, 27.2% underestimated and 5.0% overestimated their BMI category the corresponding estimates for women were 15.3% and 19.6%, respectively. The large majority of underweight (64.3%) and obese individuals (93.1%) overestimated and underestimated their weight, respectively. Overall, 13.5% of Italians misperceived (8.9% underestimated and 4.6% overestimated) their BMI category by more than 2 kg/m. By multivariate analysis, we observed significant differences in terms of sex, education, geographic area, marital status, smoking and drinking habit, year of survey and BMI category. In conclusion, misperception of body weight is frequent in Italy, paralleling findings from other countries with more unfavourable overweight and obesity patterns. The fact that one out of three Italian adults misperceive their weight is of great concern and indicates that media intervention campaigns aimed at explaining measurement and correct interpretation of BMI are required.