PURPOSE: At many institutions chest x-rays (CXR) are routinely performed on mechanically ventilated patients on a daily basis. Among the aims of this study was the assessment of a) frequency of clinically relevant findings from routine CXR in surgical patients under mechanical ventilation, b) comparison of expectations of clinically important CXR findings with estimation of clinical relevance of findings once films were obtained, c) indications and clinical consequences of findings from CXR requested in addition to routine films. METHODS: Prospective study, 40 patients with 741 CXR. Standardised film reporting. Daily recording of clinical data by means of an evaluation score. Interview of intensive-care physicians for assessment of: what information was expected from any routine CXR? did CXR offer helpful information for further treatment planning? RESULTS: 26% of routine CXR had a considerable therapeutical impact. 43% of all routine CXR were expected to have an influence on patient management, 57% were not. 16% of those CXR that had been expected not to offer essential information, disclosed relevant findings. Of the additionally obtained CXR, 53% were performed to check position of endotracheal tube and catheters and 47% related to other indications. CONCLUSION: Critically ill surgical patients under mechanical ventilation should have daily CXR follow-up, as one-fourth of these films has an impact on the patient's management.