Objective To estimate the extent of under- and over-reporting, to examine associations with misreporting and sociodemographic and lifestyle characteristics and mental health status and to identify differential reporting in micro- and macronutrient intake and quality of diet. Design A health and lifestyle questionnaire and a semi-quantitative FFQ were completed as part of the 2007 Survey of Lifestyle, Attitudes and Nutrition. Energy intake (EI) and intake of micro- and macronutrients were determined by applying locally adapted conversion software. A dietary score was constructed to identify healthier diets. Accuracy of reported EI was estimated using the Goldberg method. ANOVA, χ2 tests and logistic regression were used to examine associations. Setting Residential households in Ireland. Subjects A nationally representative sample of 7521 adults aged 18 years or older. Results Overall, 33·2 % of participants were under-reporters while 11·9 % were over-reporters. After adjustment, there was an increased odds of under-reporting among obese men (OR = 2·01, 95 % CI 1·46, 2·77) and women (OR = 1·68, 95 % CI 1·23, 2·30) compared to participants with a healthy BMI. Older age, low socio-economic status and overweight/obesity reduced the odds of over-reporting. Among under-reporters, the percentage of EI from fat was lower and overall diet was healthier compared to accurate and over-reporters. The reported usage of salt, fried food consumption and snacking varied significantly by levels of misreporting. Conclusions Patterns in differential reporting were evident across sociodemographic, lifestyle and mental health factors and diet quality. Consideration should be given to how misreporting affects nutrient analysis to ensure sound nutritional policy.