Objectives: To measure total energy expenditure (TEE) and total body water (TBW) in healthy Swedish children 9 or 14 months of age. To compare their TEE with current recommendations for energy intake. To define their body composition and relate this to energy expenditure. Design: Children were investigated at 9 or 14 months. The following variables were measured: TEE and TBW (by the doubly labelled water method), weight and length. Total body fat (TBF), sleeping metabolic rate, activity energy expenditure and physical activity level (PAL) were calculated. Subjects: Thirty infants 9 months of age and 29 children 14 months of age. Results: TEE was 323 AE 38, 322 AE 29, 313 AE 23 and 331 AE 28 kJ=kg=day in 9-month-old girls, 9-month-old boys, 14-month-old girls and 14-month-old boys, respectively. At 9 months of age girls and boys contained 29.6 AE 4.8 and 29.7 AE 4.5% TBF, respectively. At 14 months the corresponding figures were 29.1 AE 4.3 and 28.2 AE 4.3%. There was a significant negative relationship between PAL and %TBF (r ¼ 70.81, P < 0.001, n ¼ 59). Conclusions: Measured TEE plus calculated energy cost of growth confirm previous estimates that the physiological energy requirements of children 9 and 14 months of age are 15 -20% lower than current recommendations for energy intake. One possible interpretation of the relationship between PAL and %TBF is that children with a high TBF content are less physically active than children with less TBF. However, this relationship needs further studies.