The appropriate surgical approach for a large mediastinal tumor is controversial. Median sternotomy is the standard approach for thymomas. We herein report the case of a giant thymoma, 13 cm in diameter, surgically resected via anterolateral incision. Subsequent thymectomy was performed via thoracoscopy. The resected specimen was a WHO type AB thymoma, Masaoka stage I, without capsular invasion. The anterolateral incision was less invasive and more versatile in the present case, as the incision could be extended to a hemiclamshell or posterolateral incision depending on exposure and relationship to adjacent organs and vascular structures.