Chest CT has been proposed as a surrogate outcome measure in the evaluation of cystic fibrosis lung disease. Quantitative evaluation of chest CT findings requires application of a scoring system to derive numerical values. Several scoring systems are in use. These mostly rely on a subjective judgement of the severity and extent of various features of cystic fibrosis lung disease, including bronchiectasis, bronchial wall thickening, mucous plugging and air-trapping. Scores can subsequently be added to produce a total score. The precision or reproducibility of scoring systems has been assessed but with heterogeneous statistical approaches. Total scores appear to have high levels of reproducibility, but this might mask poorer levels of agreement for individual observations and component scores. It can also be questioned whether total scores are biologically meaningful, as compared to assessments of individual features. Various studies suggest that CT scores give an accurate indicator of the severity of disease, and CT scores might be the best predictors of long-term outcome, but data in this area are limited. CT scores are more sensitive than traditional lung-function indices such as FEV; however the lung clearance index, by multiple breath washout, appears to offer comparable sensitivity to CT. It is not clear whether CT scores are adequately responsive to changes in disease severity in the short to medium term; this is a challenge to the use of CT as a surrogate outcome measure for clinical trials of therapies specific to cystic fibrosis. Cystic fibrosis scoring would benefit from greater levels of standardisation in terms of CT techniques, scoring system, training of observers and measures of reproducibility. Automated approaches to quantifying CT parameters might also offer improved precision. The benefits of chest CT must be weighed against the principal drawback of radiation exposure. The case for more widespread use of chest CT would be strengthened if precision of CT scoring were improved.