Nutritional status must be closely monitored in cystic fibrosis (CF) patients. This study compared three methods of measuring body composition in CF patients and then examined the relationships between two simple anthropometric markers of nutritional status - tricipital skinfold thickness (TSK) and arm muscular circumference (AMC) - and the results given by each method. Fifty-five patients with CF, 27 females and 28 males, participated in this study. The mean age at the time of the study was 14 ± 5 years, ranging from 4 to 29 years. The four skinfolds (SK) and arm circumference were measured in all patients and fat mass (FM) and AMC were calculated. Fifty patients underwent dual energy x-ray absorptiometry (DEXA) and 38 underwent bioelectrical impedance analysis (BIA). The values for FM as calculated by the three methods were highly correlated, as were the values for lean body mass (LM) (p<0.001). The LM assessed by anthropometry was overestimated by 8 ± 4% compared with DEXA and by 6 ± 7% compared with BIA. BIA overestimated LM by 4 ± 6% compared with DEXA (p<0.001). The LM values measured by SK, DEXA, and BIA were highly correlated with AMC (p<0.001) and FM calculated using these three techniques were highly correlated with TSK (p<0.001). The measurement of TSK and AMC are simple and rapid ways to evaluate body composition. The excellent correlation between the three methods used to measure body composition suggests that they are valid for use in patients with CF, but the results were not identical. The measurement from each technique must be interpreted according to its own norms and comparisons can only be made if the same technique is used in the same patient.