Cystic fibrosis (CF) is a systemic disorder that may compromise linear growth in childhood, but quantitating this effect requires accurate mathematical models for normal growth. Anthropometric measurements on a cohort of 37 CF patients were analyzed using the growth model of Preece and Baines (1978) which reduces longitudinal height data to 6 quantitative parameters. When parameter means for CF females (n = 19) were compared to the reference population in the Harpenden growth study, the overall difference was significant (p less than 0.05). Examination of the derived biological parameters revealed 12-month and 14-month delays in age at take off and peak height velocity, respectively, indicating that the pubertal growth spurt in female patients is delayed. Mean ages at take off and peak height velocity were delayed 9 months in the CF males (n = 18). These results reaffirm the observation that CF females experience greater morbidity in later childhood and adolescence than males, and illustrate a quantitative approach that should facilitate further examination of CF and the efficacy of different treatment modalities on the disease process in both sexes.