In adults, the course and outcome of the acquired respiratory distress syndrome (ARDS) are closely related to the initial respiratory situation. Respiratory indices are frequently used for prognostic purposes and hence for the institution of new techniques such as extracorporeal lung support. The validity of these indices to predict the outcome in pediatric ARDS patients has not been examined as yet. We studied respiratory indices in 69 pediatric ARDS patients. METHODS. Out of 69 pediatric ARDS patients with various underlying diseases (Table 1), we chose 21 with a paO2/FiO2 ratio less than 150 mm Hg at some point to test the prognostic significance of a respiratory severity index (RSI), i.e., mean airway pressure x alveolar-arterial pO2 difference (A-aDo2)/paO2, a respiratory index (RI), i.e., A-aDO2-paO2/paO2, and other respiratory parameters (Table 2). Postsurgical patients, patients with incurable diseases, clearly non-respiratory deaths, and those treated with extracorporeal membrane oxygenation were excluded. We looked for statistical differences between survivors and nonsurvivors and correlations between ventilator days, intensive care unit (ICU) days, and hospital days and these indices. RESULTS. We did not find a significant difference between all respiratory indices tested at admission to the ICU and 24 h later between survivors and nonsurvivors (Table 3). Nonsurvivors initially had significantly higher blood pressures and lower heart rates. Both RSI and RI were significantly correlated to days on the ventilator, days in the ICU, and days in the hospital (Table 4). Initial multiorgan failure was significantly more common in nonsurvivors. CONCLUSIONS. Initial lung dysfunction as indicated by respiratory indices does not predict the outcome in pediatric ARDS. The underlying disease, hemodynamic situation, and age have to be considered in relation to the degree of lung dysfunction to determine new therapeutic strategies such as extracorporeal support.