Pretherapeutic T4 staging of centrally located lung cancer is crucial for the treatment strategy, but non-invasive imaging techniques are of low accuracy. We have developed the new imaging technique of intraoperative mediastinoscopic ultrasound (MUS) to predict technical resectability in tumors staged cT4 based on computed tomographic scanning.Intraoperatively, a sterilizable fingertip ultrasound probe is introduced and guided through the video mediastinoscope with a modified grasper during staging mediastinoscopy. The position of the probe in front of the tracheobronchial tree and in direct contact with the vena cava and pulmonary artery reduces air interference. We reviewed the results for 24 patients with tumors staged cT4 between July 2002 and January 2006. For 18, the prediction of MUS concerning resectability could be compared with intraoperative findings at the time of thoracotomy.MUS visualizes all central vessels and their relation to the tumor with high accuracy. The pulmonary artery and pulmonary veins are displayed not only in their central parts but also in their interlobar branches. Of the 24 patients, 18 proceeded to thoracotomy after conclusive MUS and had tumors proved to be technically resectable in accordance with prediction by MUS. Comparison of cT (computed tomographic scan), cT (MUS) and pT revealed that T stages defined by MUS accurately predict pathologic T stages.MUS allows investigators to assess infiltration of the great vessels and the mediastinum, especially in right-sided tumors. MUS will supplement endoscopic ultrasound-guided fine needle aspiration for the right upper mediastinum in staging of centrally located tumors.