Insertion of an endotracheal tube into the esophagus is an infrequent but life-threatening complication of endotracheal intubation. This complication is difficult to detect on standard, anteroposterior, portable chest radiographs because the incorrectly placed endotracheal tube is usually projected over the tracheal air column. To evaluate the use of chest radiographs to detect the malposition, we performed a two-part study. First, we analyzed the findings on chest radiographs in six patients in whom an endotracheal tube had been inserted in the esophagus, and then we analyzed 328 portable chest radiographs of patients with both endotracheal and nasogastric tubes to determine the best radiographic position for identifying the exact location of an endotracheal tube. The findings in the six patients included projection of the tube lateral to the trachea (five patients), gastric distension (four patients), esophageal air (two patients), and deviation of the trachea by the balloon cuff (one patient). The study of the portable chest radiographs showed that the endotracheal tube position could be identified correctly in 81 (92%) of 88 of the films made with the patient in a 25 degrees right posterior oblique position. The trachea and esophagus were superimposed in 25 (96%) of 26 of the radiographs made with the head turned to the left and with the patient in a 25 degrees left posterior oblique projection. Our results show that by positioning patients for chest radiographs in a 25 degrees right posterior oblique position, the location of endotracheal tubes can be identified accurately.