Despite the important role of lymph node infiltration for the classification and prognosis of non-small-cell lung cancer (NSCLC), no standards exist to evaluate the quality of mediastinal lymphadenectomy. Researches at several centers are not convinced that complete ipsilateral lymphadenectomy is necessary. We investigated 270 consecutive patients undergoing a potential curative operation for NSCLC including complete ipsilateral lymph node dissection in order to ascertain whether or not there is a correlation between tumor localization and lymph node infiltration. Patients were classified into the UICC (1987) stages I (n = 115), II (n = 42), and IIIa (n = 113). In patients with N1-positive lymph nodes (n = 61) we found higher 5-year survival for patients with only intrapulmonary lymph node infiltration (39%) than for patients with hilar infiltration (21%). Patients with N2 disease showed skip metastases in up to 81% of cases. We found that no tumor location predicted the lymph node infiltration. Due to the variability of lymph node infiltration and the frequently occurring skip metastases, complete ipsilateral lymphadenectomy should be the standard for curative operations for NSCLC.