Despite an apparently curative resection, about 30-40% of the patients with pT1-3, pN0, M0 non-small cell carcinomas (NSCLC) will relapse after surgery. Therefore, it has to be assumed that in some patients a tumor cell dissemination has occurred already at the time of surgery. By using sensitive immunocytochemical techniques, the extent of an early regional and/or systemic tumor cell dissemination can be demonstrated. In pN0 patients, an early lymphatic dissemination can be detected in 15.2% of the cases and a systemic spread of tumor cells into the bone marrow in 54.3%. Since systematic mediastinal lymphadenectomy does not significantly improve the long-term prognosis in these patients, a systemic adjuvant therapy should be offered to patients at risk with a stage I NSCLC.