Objective: To evaluate the relative incremental cost of complications after lobectomy for stage I non-small cell lung cancer (NSCLC). Methods: 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. Results: 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). Conclusions: 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.