Desire for weight change and level of dietary consciousness may severely bias reported food intake in dietary surveys. We evaluated to what degree under- and overreporting of energy intake (EI) was related to lifestyle, sociodemographic variables, and attitudes about body weight and diet in a nationwide dietary survey. Data were gathered by a self-administered quantitative food-frequency questionnaire distributed to a representative sample of men and women aged 16-79 y in Norway, of whom 3144 subjects (63%) responded. Reported EI was related to estimated basal metabolic rate (BMR) based on self-reported body weight, age, and sex. An EI:BMR < 1.35 was considered to represent underreporting and an EI:BMR > or = 2.4 as overreporting of EI. Fewer men than women underreported EI (38% compared with 45%). The fraction of overreporters did not differ significantly between sexes (7% of the men compared with 5% of the women). A large proportion of underreporters was obese (9%) and wanted to reduce their weight (41%). Few overreporters were obese and 12% wanted to increase their weight. Underreporters consumed fewer foods rich in fat and sugar than did the other subjects. Multiple regression analysis showed that desire for weight change and physical activity score were significantly correlated with both EI and EI:BMR when adjusted for sociodemographic and lifestyle variables. Our findings indicated that attitudes about one's own body weight influenced reported EI. These attitudes are important in the interpretation of dietary data because many of the subjects (> 30%) wanted to change their body weight.