The pathophysiologic manifestations of cystic fibrosis are continually evolving as more patients survive into their adult years. Although the correlation between chest roentgenographic appearance and pulmonary function testing is well described in children with cystic fibrosis, to our knowledge, there are no data that evaluate this relationship in adults. We analyzed 66 paired studies of chest roentgenographic appearance (Brasfield score) and spirometry in 27 adults with cystic fibrosis between the ages of 18 and 40 years. There was a very good correlation between spirometry and the Brasfield score in adults with cystic fibrosis. The strongest correlation was between the percent predicted FEV1 and the Brasfield score (r = 0.68, p less than 0.001). These correlations were found to remain significant in the patients in whom longitudinal data were available. The FEV1 declined 104 +/- 26 ml/yr in 11 patients who were followed up for a mean duration of 5.8 +/- 0.5 years. The decline in FEV1 per year in adults with cystic fibrosis was significantly greater than in nonsmoking or smoking adults of similar age.