The extent of lymphadenectomy in the treatment of non-small cell lung cancer is still a matter of controversy. While some centers perform mediastinal lymph node sampling with resection of only suspicious lymph nodes, others recommend a radical, systematic mediastinal lymphadenectomy (LA) to improve survival and achieve a better staging. Herein we report on the impact of LA on tumor staging in a controlled, prospective, randomized clinical trial comparing lymph node sampling and LA in a total of 182 patients with operable non-small cell lung cancer. Regardless of the type of lymphadenectomy performed, the percentage of patients with pathologic N1 or N2 (sampling: n = 23, 23.0%; LA: n = 22, 26.8%) disease was very similar in both groups, indicating that systematic radical lymphadenectomy is not an essential prerequisite to determine the N stage of a patient. In contrast, the number of patients detected to have lymph node involvement at multiple levels was significantly increased by LA. In the lymph node sampling group only 4 of 23 patients (17.4%) with N2 disease were found to have more than one lymph node level involved, whereas LA results in the detection of excessive N2 disease in 12 of 21 patients (57.2%; p = 0.007), which was associated with a shorter distant metastases-free (p = 0.021) and overall survival. In conclusion, LA is not essential to determine the N stage of a patient, but results in a more detailed staging of the N2 region, which is of prognostic significance. Therefore, it might be useful to identify patients with a higher risk for tumor relapse.