Objective: To identify and describe characteristics of the bias of reported energy intake of participants in the Gothenburg Osteoporosis and Obesity Determinants (GOOD) study. Design: A validated diet history with a detailed questionnaire and an interview was used. Body fat was analysed by dual-energy X-ray absorptiometry. The ratio of energy intake (EI) to BMR was used to define under-reporters (EI:BMR , 1?30), acceptable reporters (EI:BMR $ 1.30 to ,2.64) and over-reporters (EI:BMR $ 2.64). Setting: Sahlgrenska University Hospital, Gothenburg, Sweden. Subjects: A total of 695 males (18-20 years). Results: Sixty-eight per cent were classed as acceptable reporters, 22 % as overreporters and 10 % as under-reporters. The under-reporters had higher BMI and body fat percentage than acceptable reporters (P , 0?001), while over-reporters had lower BMI and body fat percentage (P , 0?001). Over-reporters had more frequent use of protein supplements than acceptable reporters and higher physical activity. Over-reporters had a more regular and under-reporters a less regular meal pattern compared with acceptable reporters. Conclusions: Important knowledge of dietary reporting bias in a previously sparsely studied population has been provided. Over-reporting of energy intake was more common than under-reporting in the present population of young men and characteristics of under-and over-reporters were identified. The GOOD study was initiated with the central aim to determine environmental and genetic factors involved in the regulation of bone and fat mass, and the nutrient data of the acceptable reporters can be used for further investigation of the health effects of energy and nutrient intake. Virtually all dietary assessments are based on self-reported dietary intake, which is frequently biased, resulting in over-or underestimation of the actual energy intake (1) . If subjects are in energy balance, i.e. weight-stable, the energy intake must correspond to the total energy expenditure. The doubly labelled water (DLW) technique is considered the 'gold standard' for determining total energy expenditure (2) ; however, the method is expensive and therefore not used in large studies. As an alternative method for detecting misreported energy intake the Goldberg cut-off (3) can be used. In a review, Black et al. (1) concluded that underreporting and under-eating occur in most dietary assessments, but with varying frequency according to the dietary assessment method used. Several characteristics of under-reporters, such as high BMI, high body fat percentage, food-specific reporting, low intake of fat, and high intake of protein and micronutrients, have been presented (4)(5)(6)(7)(8)(9)(10)(11)(12)(13) .Only a few studies have investigated the frequency and characteristics of over-reporting. Young, lean males have been found to be a group with a relatively high prevalence of over-reporting (9,12) , but data are sparse. The interpretation of relationships between diet and other variables can lead to false conclusions if bias ...