To evaluate the relative incremental cost of complications after lobectomy for stage I non-small cell lung cancer (NSCLC). Patients treated with open or video-assisted thoracoscopic surgery (VATS) lobectomy for stage I NSCLC between 2008 and 2014 were selected. A patient registry was queried for all complications recorded during a 90-day postoperative interval. Hospital cost data for each patient was concatenated with clinical data. Linear regression was used to assess the impact on direct hospital costs of specific complications. Among the 488 patients included in this study, 34% experienced ≥1 complication and 17% experienced ≥1 major complication. In patients experiencing complications, atrial arrhythmia (13%), prolonged air leak (8.6%), atelectasis (6.4%), and transfusion requirement (4.5%) were most common. Minor complications increased the relative cost of lobectomy by 29% (95% confidence interval [CI], 23%-34%; P < .001) compared to the cost of an uncomplicated lobectomy. Major complications increased costs by 57% (95% CI, 53%-62%; P < .001). The greatest predictor of increased 90-day cost was major pulmonary complications, which increased cost by 111% (95% CI, 96%-126%; P < .001). Prolonged air leak increased relative mean cost by 22% (95% CI, 10%-33%; P < .001) and pneumonia by 96% (95% CI, 75%-117%; P < .001). Complications, both major and minor, contribute significantly to the total 90-day direct hospital cost of lobectomy for stage I NSCLC. Analysis of 90-day postoperative outcomes more accurately captures costs. Major pulmonary complications, atrial arrhythmia, pneumonia, and prolonged air leak represent 4 high-yield targets for cost reduction. Efforts to control health care spending while improving patient outcomes might optimally focus on reducing complications that incur the greatest relative incremental cost. Copyright © 2017 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.