Nowadays, hyperbaric oxygen therapy is a completely accepted therapy for several diseases. It consists in providing a high pressure environment, with 100% oxygen, in order to increase tecidual pO2. The main complication of this procedure is middle ear barotrauma. Because of the conditions of the patients that undergo hyperbaric therapy, the complaints are not reliable, therefore, a careful assesment of ear conditions is mandatory. We carried out a study in 21 patients undergoing hyperbaric therapy, trying to determine the alterations in the middle ear, and the predisposing factors of these alterations.We found evidence of barotrauma in 5 patients after the first session and in 8 patients after the 5th session.The patients with orotraqueal intubation seemed more likely to have middle ear barotrauma.There was little correlation between the patient's complaints and the otoscopic findings. Therefore, we concluded that middle ear barotrauma is a frequent complication of hyperbaric therapy, and suggest that all patients undergoing this procedure have careful investigation of possible middle ear alterations.