A long-term study has been performed on 285 lung perfusion scintigrams obtained from 113 patients with cystic fibrosis. Transverse and longitudinal comparisons with clinical and radiological scores, as well as retrospective analysis of the deceased patients, were the methods used in order to evaluate the importance of the scintigraphic images. It appears that lung scintigraphy is the best index of the regional lung impairment, and contributes, as does a chest radiograph, to the early detection of lung lesions, the two methods being complementary. The survival rate of CF patients reached 0.80 at 9 yr when initial scintigraphy was normal or only moderately impaired, but fell to 0.18 when severe lesions were seen on the first scintigrams.