To assess the nutritional status of children and adolescents with bronchiolitis obliterans. Study of 57 children and adolescents. Nutritional status was assessed (for children using z scores for weight/age, stature/age, weight/stature and for adolescents using stature/age and body mass index (BMI) percentiles), and so was body composition (using tricipital skin folds, subscapular skin folds and the sum of both plus the muscular circumference of the arm) and pulmonary function was assessed in subjects over 8 years old. The high percentages of malnutrition and risk of malnutrition are of note: 21.7%, 17.5%. Among the children, weight/age and stature/age detected higher percentages of malnutrition, 21.6%, 16.2%, whereas weight/stature underestimated this diagnosis. Among the adolescents, BMI detected a high percentage of malnutrition (25%) and of risk of malnutrition (20%). Body composition analysis detected 51% with low muscle reserves and the majority of patients had normal fat reserves. Compromised pulmonary function was associated with poor performance at exercise (r = 0.434; p = 0.024). Malnutrition and/or nutritional risk and low muscle reserves were significantly associated with the 6-minute walking test (p = 0.032; p = 0.030). There was no association between spirometry and the nutritional variables (p>0.05). These results emphasise the need for nutritional intervention, and that in addition to using weight and height indices for nutritional assessment it is necessary to combine these with an analysis of body composition, so that a larger number of patients with malnutrition and/or at an increased risk of developing malnutrition may be identified and correctly managed.