To reduce or omit a mediastinal lymph node dissection in the patients with clinical stage I non-small cell lung cancer (NSCLC), several authors examined the prevalence of metastatic sites of lymph nodes. Because lymphatic drainage usually heads for the upper mediastinum in upper lobe cancer and for the lower mediastinum in lower lobe cancer, upper and lower mediastinal lymph node dissection could be reduced in lung cancers of lower lobe and upper lobe. By using sentinel node (SN) navigation surgery, it is possible to omit mediastinal lymph node dissection. Radiological findings are also useful to determine reduction of mediastinal lymph node dissection. In clinical stage Ia adenocarcinomas that show ground glass opacity (GGO) findings on computed tomography (CT) or negative for fluorodeoxyglucose accumulation on positron emission tomography (PET), mediastinal lymph node dissection can be omitted, because these types of adenocarcinomas rarely metastasize to the lymph nodes. By using these procedures, mediastinal lymph node dissection can be reduced or omitted with little risk of local recurrence.