PURPOSE: To compare the incidence and clinical characteristics of infants with atypical CLD and those with classic BPD among premature infants less than 32 weeks' gestation. METHODS: Clinical data was collected retrospectively from the 256 premature infants less than 32 weeks' gestation and their mothers during 3-year study period. RESULTS: Among 212 preterm infants less than 32 weeks' gestation who survived to 28 days of life, 19 (9%) had atypical CLD and 38 (17.9%) had classic BPD. Atypical CLD infants were significantly heavier and more mature than classic BPD infants (mean birth weights, 1,100+/-294 g vs 915+/-225 g; and mean gestational age, 26.9+/-1.6 weeks vs 21.1+/-1.3 weeks). Duration of ventilator therapy and oxygen inhalation within 28 days of age were shorter in atypical CLD infants than in classic BPD infants (mean duration of ventilator therapy, 16.3+/-6.9 days vs 27+/-6.8 days; and mean duration of oxygen inhalation, 25.5+/-13.5 days vs 53.8+/-39 days). Oxygen dependency in atypical CLD infants showed bimodal pattern, decreasing gradually to 3-week after birth and upturning to peak at about 5-week after birth. Comparing the respiratory indices between classic BPD and aypical CLD, FiO2 at day 2,7, and 10, and oxygen index at day 2, and 10 were significant in classic BPD, but MAP were not. Considering the birth weight, MAP per birth weight, and modified oxygen index showed more apparent differencies between the two groups. CONCLUSION: 35.5% of total CLD were atypical CLD and showed bimodal pattern in oxygen dependency. Atypical CLD infants were significantly heavier and more mature than classic BPD infants.