To ascertain the value of the daily routine chest x-ray in the medical ICU, we determined prospectively the number of unsuspected abnormalities observed on 507 consecutive chest films and the consequent management changes in 94 ICU patients. Primary diagnoses were classified as pulmonary, hemodynamically unstable cardiac, uncomplicated cardiac, or miscellaneous. Admission films and those taken after procedures or a change in clinical status were excluded. Ventilator status and the tubes and catheters visible on the films were also noted. After clinical evaluation, management plans were made by ICU physicians and then the chest x-ray was examined and unsuspected abnormalities and resulting management changes were noted. Of the 507 chest films, 76 (15%) revealed an unsuspected abnormality, 71 (93%) of which led to a management change. There were significantly (p less than .02) more unsuspected abnormalities and management changes in the pulmonary and unstable cardiac patients, independent of ventilator status. Patients with two or more catheters and/or tubes visible on the chest film also had significantly more management changes (51/312 vs. 11/150, p less than .05). We conclude that while routine chest films affect the management of pulmonary and unstable cardiac patients in the ICU, routine films rarely influence management of uncomplicated cardiac patients and those without heart or lung disease, and are not warranted in this group.