Using a dog model of prolonged translaryngeal intubation, the authors studied laryngeal injury. Segments of 10.7 mm diameter endotracheal tube were sutured in place in the larynges of anesthetized animals, and the animals were allowed to awaken and the tubes left in place for periods of 24 h to 84 days in a total of 13 dogs. Each animal's larynx was studied endoscopically at weekly intervals and at the time of death. Both endoscopic and postmortem examination revealed erythematous laryngeal mucosa at 24 h and severe mucosal ulceration by 1 week. Microscopic examination revealed mucosal inflammation at 24 h with loss of mucosal architecture by 1 week. In several animals intubated 1 week or longer, inflammatory infiltrates were present in the arytenoid cartilage. While damage was generally severe by 1 week, it did not tend to become more severe after that time. Between week 1 and week 12, there was no significant correlation of the severity of laryngeal injury with the duration of endotracheal intubation. The results suggest that duration alone may not be a factor in laryngeal injury after the first week of intubation.