PurposeTo investigate (1) the contributions of sex, age, nutritional status- and physical-fitness-related variables on health-related quality of life (HRQOL) in Spanish children with cystic fibrosis, and (2) the agreement on HRQOL between children and their parents.MethodsIn 28 children aged 6–17 years, body mass index percentile, percentage body fat, physical activity, pulmonary function, cardiorespiratory fitness, functional mobility, and dynamic muscle strength were determined using objective measures. HRQOL was measured using the revised version of the cystic fibrosis questionnaire. Simple and multiple linear regression analyses were performed to determine the variables associated with HRQOL. To assess the agreement on HRQOL between children and parents, intra-class correlation coefficients (ICCs) were calculated.ResultsGirls reported worse emotional functioning, a higher treatment burden, and more respiratory problems than boys. Greater functional mobility appeared associated with a less favourable body image and more eating disturbances. Agreement on HRQOL between children and parents was good to excellent, except for the domain of treatment burden.ConclusionsSex and age were stronger predictors of HRQOL than nutritional status- or physical-fitness-related variables. Children reported a lower treatment burden than their parents perceived them to have.