Fractional exhaled nitric oxide (FE(NO)) levels are increased in children and adults with asthma, whereas low levels have been found in cystic fibrosis and primary ciliary dyskinesia. The aim of this study was to investigate whether FE(NO) measurements could distinguish between children below the age of 2 with different airway diseases. FE(NO) measurements were performed in 118 infants aged between 4.6 and 25.2 mo: 74 infants with recurrent wheezing (RW), 24 with bronchopulmonary dysplasia (BPD), and 20 with cystic fibrosis (CF). FE(NO) was measured also in 100 healthy controls aged between 1.1 and 7.7 mo. Geometric mean (95% confidence interval) FE(NO) values were 10.4 (9.1-12.0) parts per billion (ppb) in healthy infants, 18.6 (15.6-22.2) ppb in wheezy infants, 11.7 (8.2-16.8) ppb in BPD infants and 5.9 (3.4-10.1) ppb in CF infants. FE(NO) in wheezers was higher than in controls, BPD, and CF (p = 0.009, p = 0.038, and p < 0.001, respectively). Atopic wheezers showed higher FE(NO) than nonatopic wheezers (p = 0.04). CF infants had lower FE(NO) than healthy controls and BPD infants (p = 0.003 and p = 0.043, respectively). FE(NO) values in BPD and control infants were not different. We conclude that FE(NO) is helpful to differentiate various airway diseases already in the first 2 y of life.