BACKGROUND: Unsuspected lymph node metastases are found in the surgical specimens of 10% to 25% clinical stage I lung cancers. Video-assisted thoracic surgery (VATS) is a minimally invasive alternative to thoracotomy. Because detection of clinically occult metastases is dependent on the completeness of surgical lymph node dissection, the influence of surgical approach on nodal evaluation is of interest. We determined the frequency of nodal metastases identified in clinically node-negative tumors by thoracotomy ("open") and VATS approaches to approximate the completeness of surgical nodal dissections. METHODS: The Society of Thoracic Surgery database was queried for lobectomies and segmentectomies from 2001 to 2010. RESULTS: A total of 11,531 (7,137 open and 4,394 VATS) clinical stage I primary lung cancers were resected. Nodal upstaging was seen in 14.3% (1,024) in the open group and 11.6% (508) in the VATS group (p<0.001). Upstaging from N0 to N1 was more common in the open group (9.3% versus 6.7%; p<0.001); however, upstaging from N0 to N2 was similar (5.0% open and 4.9% VATS; p=0.52). Among 2,745 propensity-matched pairs, N0 to N1 upstaging remained less common with VATS (6.8% versus 9%; p=0.002). CONCLUSIONS: During lobectomy or segmentectomy for clinical N0 lung cancer, mediastinal nodal evaluation by VATS and thoracotomy results in equivalent upstaging. In contrast, lower rates of N1 upstaging in the VATS group may indicate variability in the completeness of the peribronchial and hilar lymph node evaluation. Systematic hilar dissection is encouraged, particularly as more surgeons adopt the VATS approach.