We report on a rare case of substernal thyroid carcinoma extending into the posterior mediastinum of a 48-year-old man. The tumor was resected by partial sternotomy and a small anterior thoracotomy, combined with video-assisted thoracoscopy. The pathological diagnosis was of a well differentiated papillary adenocarcinoma of the thyroid with mediastinal extension. The patient had an uneventful postoperative course and no recurrence of tumor 6 months after surgical treatment. We describe this surgical approach and discuss the advantage for cervicothoracic tumors extending into the posterior mediastinum.