BACKGROUND The clinical value of routine chest X-rays in critical care has been questioned, but has not been studied in the trauma environment to date. The objective of this study was to identify easy to use clinical predictors of utility in this setting. METHODS A prospective observational study was made in an 8-bed traumatology ICU. Severe trauma patients (ISS > 15), aged 15 or older and admitted for 48 h or longer were included. Pregnant women and radiographs obtained during initial care or for reasons other than routine indication were excluded. A staff physician, separated from clinical duties, independently reviewed the films in search of changes, as described in a closed checklist. Following closed criteria, the attending physicians reported previous day clinical events and changes in clinical management after chest X-ray obtainment. Demographic and epidemiological data were also recorded. The associations among variables were studied by univariate and multivariate analysis. RESULTS A total of 1440 routine chest X-rays were obtained from 138 consecutive patients during one year. Young males prevailed (82%; 39 ± 16 years). The most common process was severe blunt trauma (97%). Fifty-two percent suffered severe chest trauma. The mean length of stay was 12.9 ± 10.1 days. Mechanical ventilation was used in 86.8% of the cases. A median of 10.4 ± 9.3 films were obtained from each patient. A total of 14% of the X-rays showed changes, most commonly malpositioning of an indwelling device (6.8%) or infiltrates (4.9%). Those findings led to a change in care in 84.6% of the cases. Multivariate analysis identified the following significant (p < 0.05) risk factors for radiographic changes: first two days of evolution, mechanical ventilation, worsening of PaO₂/FiO₂, worsening of lung compliance and changes in respiratory secretions. CONCLUSIONS Based on the results obtained, the risk of not identifying dangerous conditions by restricting routine chest X-rays prescription to the described conditions is low. Observing this policy would probably mean substantial savings and a reduction in radiation exposure.