Wheezing is a common finding in infants with cystic fibrosis (CF). This study was undertaken to determine the prevalence of wheezing in infants with CF and to compare the clinical outcome of those who wheezed in infancy with that of those who did not. The study cohort included 229 CF patients born between 1965 and 1979 with CF diagnosed before 2 years of age. Fifty-seven (25%) had physician-documented wheezing during the first 2 years of life. Wheezing had resolved by the age of 2 years in 50% of the patients and by the age of 4 years in 75%. Although wheezing seemed to be linked to a family history of allergy and asthma, the frequency of the delta F508 mutation was similar to that of the non-wheezers. There was no significant difference in survival at the age of 13 years between the two groups. At the age of 7 years, patients who had wheezed had significantly lower forced expiratory flow rate at mid-expiratory phase (85 +/- 34% predicted) compared with those with no wheezing history (101 +/- 34% predicted). At the age of 13 years, forced expiratory volume in 1 second values was lower in the wheezing group (69 +/- 24% predicted vs 78 +/- 21% predicted), as was forced expiratory flow rate at mid-expiratory phase (56 +/- 33% predicted vs 69 +/- 30% predicted). In conclusion, although wheezing in infants with CF seems to have diminished with age, pulmonary function abnormalities were more evident at 7 and 13 years of age in the group that wheezed than in the group that did not.