['Patients with T4 non-small cell lung cancers with limited involvement of mediastinal structures can undergo resection, with acceptable long-term survival. Computed tomography has not proven to be reliable in determining the operability of locally advanced lung carcinoma. This study evaluated the ability of video-assisted thoracoscopy alone and with endothoracic sonography to determine operability.', 'Computed tomography showed a close contact of the tumor with mediastinal structures (T4) in 155 patients. Staging was expanded with video-assisted thoracoscopy, followed by thoracoscopic ultrasound. Lateral thoracotomy with hilar and mediastinal dissection was considered the gold standard in determining operability.', 'Thoracoscopic ultrasound, compared with thoracoscopy alone and computed tomography, had the highest sensitivity (94.1% vs 75.2% vs 43.6%, p < 0.001) and specificity (98.1% vs 57.4% vs 37.0%, p < 0.001) for determining operability. Computed tomography, thoracoscopy, and thoracoscopic ultrasound were falsely negative in 57 (36.8%), 25 (16.1%), and 6 (3.9%) patients and falsely positive in 34 (21.9%), 23 (14.8%), and 1 (0.6%). False-negative results for operability by thoracoscopic ultrasound were found only in tumors involving the left atrium (3.9%).'] Does endothoracic sonography improve the estimation of operability in locally advanced lung cancer?