Background: Height evaluation is an integral part of cystic fibrosis (CF) care. Height is compared with reference values by converting it to height-for-age (HFA) z scores. However, HFA z scores do not adjust for genetic potential (ie, target height [TH]), which could result in an incorrect estimation of the height. Materials and Methods: To evaluate the magnitude of this potential problem, we assessed the agreement between HFA and HFA-adjusted-for-TH (HFA/TH) z scores in 474 Dutch children with CF. Results: In this study sample, HFA z scores were −0.07 (95% confidence interval, −0.02 to −0.12) lower than HFA/TH z scores. When HFA and HFA/TH z scores were subdivided into 4 categories (≥0, <0 and ≥–1, <−1 and ≥−2, and ≤−2), a moderate agreement was found. HFA z scores were classified lower than HFA/TH z scores in 21% of the measurements and higher in 15% of the measurements. Conclusion: In clinical routine, height evaluation based on HFA may result in underestimation or overestimation of height growth, which may induce inappropriate nutrition interventions.