Introduction 1 2 3 4 5 6 Methods 1 7 8 2 2 9 Table 1 Baseline patient characteristics and cause for respiratory failure  n n p Median age (months; range) 15.2 (0–127.2)  6.1 (0–217.7) c Males 14 (58.3%) 199 (62.8%) d Median PRISM II score (range) 13.5 (0–40)  9.0 (0–47) c Sepsis  3 (12.5%)  52 (16.4%) e Lower respiratory tract infection 18 (75%) 130 (41%) d Upper respiratory tract infection  1 (4.2%)  23 (7.3%) e Congenital heart disease  1 (4.2%)  22 (6.9%) e a  0  53 (16.7%) e b  1 (4.2%)  37 (11.7%) e a CNS disorders b Others c d 2 e 8 10 Results 2 Table 2 OR CI Possible confounder OR 95% CI None  9.4 3.9–22.6 PRISM II score  9.6 3.9–23.6 Sepsis 12.2 4.9–30.6 Lower respiratory tract infection 10.8 4.3–26.9 We excluded patients who died in the first 24 h after admission. This might have caused a selection bias. Therefore PICU deaths during the first 24 h of admission were analyzed for ALI/ARDS: 36 in the control group, none of whom met the ALI/ARDS criteria. No CDS died in the first 24 h after admission. Thus the odds of developing ALI in CDS are about 9 times those in controls, and this cannot be attributed to the presence of confounders. Discussion 11 The results of this study need to be interpreted with caution due to the retrospective design and the relatively low number of CDS. The results need to be confirmed in a prospective multicenter study in a larger cohort. Due to the small number of CDS admitted annually to our unit we included CDS for a longer period of time (1998–2005) than the control group (1998–2001). This may interfere with the comparability of the study groups. However, medical care on our unit did not change substantially during this extended period. In both study periods respiratory care was based on the same clinical protocols with a low tidal volume ventilation strategy. Identical ventilators were used. In addition, the disease severity (expressed as mean PRISM II scores) did not differ between 2001–2005 and 1998–2001. Therefore we have no reason to assume that the incidence of ALI in mechanically ventilated patients changed substantially during the 2001–2005 period. 11 12 p n 13 14 15 16 17 18 19 20 21 22 23 In conclusion, we found an unexpected high incidence of ALI and ARDS in CDS. The explanation for these findings remains to be elucidated.