The American College of Surgery Oncology Group Z0030 study was a prospective randomized study that showed that mediastinal lymph node sampling (MLNS) offered similar results to mediastinal lymph node dissection (MLND) in patients with non-small cell lung cancer (NSCLC). However, that study only randomized patients after thorough samplings that were negative on frozen section in several N2 and N1 nodal stations. The purpose of this study was to evaluate the effect of MLND to the more common practice of ruling out N2 disease preoperatively and then resection without sending lymph nodes for frozen section. This is a retrospective study of patients clinically staged as N0 with NSCLC. The incidence of pathologic N2 disease reported by the Society of Thoracic Surgeons (STS) database was considered to represent MLNS and it was compared with our patients who underwent complete MLND. Between January 2002 and December 2009, 1,358 patients clinically staged as N0 underwent lobectomy or segmentectomy and MLND (not MLNS). Our incidence of pathologic N2 disease in 1,107 patients who underwent lobectomy was 10.6% compared with 9.4% in the 24,896 STS lobectomy patients (p = 0.196). Our incidence of pathologic N2 disease in 251 patients who underwent segmentectomy was 13.0% compared with 5.3% in the 2,150 STS segmentectomy patients (p < 0.001). When complete MLND is performed in patients during pulmonary resection who are clinically node negative (have benign N2 nodes after selective endobronchial or esophageal ultrasound or mediastinoscopy) without using intraoperative frozen section of N2 or N1, more patients are pathologically staged with N2 disease; thus, more are considered for adjuvant chemotherapy. The impact on survival in these patients is unproven. © 2012 The Society of Thoracic Surgeons.