The present study investigates the prevalence of misreporting of energy in the Malmö Diet and Cancer cohort, and examines anthropometric, socio-economic and lifestyle characteristics of the misreporters. Further, the influence of excluding misreporters on risk estimates of post-menopausal breast cancer was examined. Information of reported energy intake (EI) was obtained from a modified diet history method. A questionnaire provided information on lifestyle and socio-economic characteristics. Individual physical activity level (PAL) was calculated from self-reported information on physical activity at work, leisure time physical activity and household work, and from estimates of hours of sleeping, self-care and passive time. Energy misreporting was defined as having a ratio of EI to BMR outside the 95 % CI limits of the calculated PAL. Logistic regression analysed the risk of being a low-energy reporter or a high-energy reporter. Almost 18 % of the women and 12 % of the men were classified as low-energy reporters, 2.8 % of the women and 3.5 % of the men were classified as high-energy reporters. In both genders high BMI, large waist circumference, short education and being a blue-collar worker were significantly associated with low-energy reporting. High-energy reporting was significantly associated with low BMI, living alone and current smoking. The results add support to the practice of energy adjustment as a means to reduce the influence of errors in risk assessment.