['The objective of this study was to document alterations in resting energy expenditure (REE), energy intake, and body composition that occur during admission for management of a pulmonary exacerbation in children with cystic fibrosis.', 'A prospective study of 14 children with cystic fibrosis (8 male, 12.5 +/- 3.3 years) was conducted throughout a 14-day hospitalization and again 3 weeks after discharge. Repeated measures analysis of variance was used to examine the change in variables across time.', 'Significant increases were documented from days 1 to 14 in weight (37.1 +/- 13.1 kg to 38.4 +/- 13.5 kg) and pulmonary function (forced expiratory volume in 1 second: 67.6% +/- 19.8% to 78.5% +/- 24.5%). Energy intake was not different between hospitalization and follow-up and averaged 175% of the Recommended Dietary Allowance. REE on day 1 was elevated (122% +/- 11% predicted); however, when expressed with fat free mass as a covariate, no significant changes were noted in REE throughout the eight measurements.'] Is acute pulmonary exacerbation associated with increased energy expenditure in children with cystic fibrosis?