Under- and over-reporting of energy intake are problems in dietary intake assessment. This study was conducted to assess the correlates of under- and over-reporting of energy intake in Tehranians. Dietary data on 947 participants (415 males and 532 females) of the Tehran Lipid and Glucose Study was collected by trained interviewers using two 24-hour recalls. Weight and height were measured by digital scale and tape measure according to standard protocols and recorded to the nearest 100 g and 1cm, respectively. Under-, normal- and over-reporting of energy intake was defined as ratio of energy intake to basal metabolic rate (EI:BMR) <1.35, 1.35-2.39 and >or = 2.4, respectively. Mean +/- SD of age was 37.3 +/-14.6 and 32.9 +/-13.6 years for men and women, respectively. Men had higher EI:BMR than women (1.72 +/-0.44 vs 1.27 +/-0.44, P<0.001). EI and EI:BMR was highest in the youngest age groups in both sexes. The prevalences of under- and over-reporting were 31% and 5%, respectively. Fewer men than women underreported EI (19% vs 40%, P<0.001). The fraction of over-reporters was significantly higher in men than women (7% vs 3%, P<0.05). EI:BMR decreased with age. Under-reporters were older and had higher BMI than normal-reporters, but their educational level did not differ significantly. Over-reporters were younger and had lower BMI than normal-reporters, but their educational levels did not differ significantly. Most over-reporters had normal BMI. Smoking was more prevalent in over-reporters than in the normal-reporters (28% vs 19% in men and 6% vs 1% in women, P<0.01). The results showed a high prevalence of misreporting of energy intake in Tehran. This phenomenon is related to age, obesity and smoking habits.