Objective: The aims of the present study were (1) to evaluate the degree to which underreporting of energy intake by repeated 24-hour recalls was related to gender, age, weight status, day of interview, educational level, smoking habits and area of living, and (2) to compare the dietary characteristics of underreporters with those of others. Design: Cross-sectional study. Ten 24-hour recalls were performed during a one-year period. Setting: The Va Èsterbotten intervention programme of cardiovascular disease and diabetes in Northern Sweden. Subjects: Ninety-four men and 99 women in four age groups: 30, 40, 50 and 60 years. Results: The prevalence of men and women with a food intake level (FIL; reported energy intake divided by estimated basal metabolic rate) below 1.2 was 44% and 47%, respectively. The youngest age group had higher FIL values than the oldest age group for both men (1.5 versus 1.1) and women (1.4 versus 1.1). The prevalence and magnitude of underreporting were directly related to body mass index (BMI; correlation coefficient: 20.47 (men) and 20.55 (women)). Smokers had a lower FIL value (1.1) than non-smokers (1.3). The nutrient density was lower for the group with high FIL values for protein and calcium and higher for fat and sucrose. The upper FIL group often had higher intake frequencies and larger portion sizes than the lower FIL group. Conclusions: Underreporting of energy intake is prevalent when 24-hour recalls are used, but the prevalence differs between sub-groups in the population. BMI was the main predictor of underreporting but also old age and smoking seem to contribute in this aspect. Socially desirable food items were not underreported to the same extent as socially undesirable food items. The intake frequencies and portion sizes partly explained the differences in FIL.