The purpose of this study was to compare estimations of daily energy expenditure (DEE.) made with a physical activity journal (PAJ) and a heart rate monitoring method (HR-VO2) in endurance athletes. Seven male cross-country skiers (21 ± 5 yr of age, mean ± SD) with high aerobic power (70.4 ± 7.2 mlO2.kg−1min−1) and eight lean and moderately active males serving as controls (22 ± 1 yr; 50.9 ± 9.9 mlO2.kg−1-min−1) were tested. VO2max, resting metabolic rate (RMR), energy cost of standardized activities, PAJ, HR monitoring, and food diaries for measurement of daily energy intake (DEI) were measured in October, before the specific training period. Results indicated that the skiers had a higher RMR (P < 0.05) than the controls (8.2 ± 1.6 vs 6.9 ± 0.6 MJ.d−1), as measured by indirect calorimetry. DEE estimates made with the PAJ anil the HR-VO2 methods were similar in the controls subjects but the HR-VO2 method yielded significantly higher results in the skiers (17.0 ± 4.0 vs 13.1 ± 2.1 MJ.d−1). DEI measurements were similar to HR-VO2 DEE in both groups. Thus, it appears that the PAJ, which was established with a sedentary population, underestimated DEE in trained cross-country skiers. Thus, the physical activity status of subjects has to be investigated before using a physical activity diary.