OBJECTIVE: To determine whether the quality of infiltrations in chest radiographs can accurately predict the histological extent of fibrotic change in patients with acute respiratory distress syndrome (ARDS). DESIGN: Retrospective clinical investigation. SETTING: Intensive care unit (ICU) of a university teaching hospital. PATIENTS AND METHODS: Of 47 patients treated with extracorporeal membrane oxygenation (ECMO) for severe ARDS over a 5-year period, 23 patients underwent open lung biopsy at thoracotomy for treatment, mostly of pneumothorax. Chest films obtained by portable chest roentgenography preceding the operation were reviewed retrospectively and compared to the histomorphological results of the lung specimen. RESULTS: Chest radiographs displayed mixed alveolar-reticular opacification in 60.2%, alveolar patterns in 22.9% and reticular opacities in 10.5%. In 0.4% there were no infiltrates, 6% could not be evaluated because of insufficient quality. There was no relevant difference between the right and left lungs. Subdividing patients into two groups according to the histological results of either absent or mild (1) or severe (2) lung fibrosis, we found an alveolar haziness in 12.3% in group 1 compared with 28.2% in group 2, while reticular characteristics were identified in 13% and 11%, respectively. CONCLUSIONS: The most common opacity in chest radiographs of patients with severe ARDS treated with ECMO is mixed alveolar-reticular opacification. Severe lung fibrosis is not positively correlated with a reticular radiographic pattern. ECMO does not lead to specific radiological changes in conventional radiograms, contrary to clinical findings that treatment with ECMO might induce pleural or pulmonic haemorrhage, especially in the earlier days when systemic heparinization had to be used instead of the heparin-coated tube-surfacing.