The incidence of postoperative chest X-ray abnormalities, arterial hypoxemia and clinically recorded pulmonary complications was studied in fifty-two 40-75-year-old men admitted for elective surgery for peptic ulcer or gallbladder disease. Twenty-eight (54%) patients had an abnormal chest X-ray and twenty-three (43%) arterial hypoxemia, whereas only four patients (8%) were identified with clinical signs and symptoms of respiratory complications. Forty-one patients (79%) were found with pulmonary complications by at least one of the three methods. Twelve patients had both an abnormal chest X-ray and arterial hypoxemia. Only two of these were identified with clinical signs indicating pulmonary complications. The great discrepancy between results based on clinical signs and symptoms noted in the patients' records and results based on postoperative chest X-ray and measurements of the arterial oxygen tension, respectively, should be of great importance when comparing the incidence of pulmonary complications after different forms of surgery and when assessing risk factors and clinical consequences of respiratory complications.