We retrospectively compared the oncologic outcome after segmentectomy versus lobectomy in patients with clinical (c-) T1a N0 M0 non-small cell lung cancer (NSCLC) detected as a part-solid ground-glass nodule or purely solid nodule on thin-section computed tomography. From 1997 to 2010, 312 patients with c-T1a N0 M0 NSCLC were determined to require a surgical approach categorized as segmentectomy or lobectomy. Preoperatively available data were collected using logistic regression analysis, and propensity matching was performed. Factors affecting local-regional recurrence were assessed by Cox proportional hazards regression analysis and Kaplan-Meier estimates. The 5-year and 10-year overall survival rates for the 80 patients who underwent segmentectomy were 97.5% and 83.5%, respectively, compared with 87.75% and 75.0%, respectively, for the 232 patients who underwent lobectomy (p = 0.019). Local-regional recurrence as the first relapse site was found in 3 the 80 segmentectomies (3.8%) of and in 15 of the 232 lobectomies (6.5%). The difference in local-regional recurrence-free survival in patients undergoing segmentectomy compared with lobectomy was not significant (p = 0.304). In 69 propensity score-matched pairs, there was no significant difference in the overall survival (p = 0.442) or local-regional recurrence-free survival (p = 0.717) between the two groups. Multivariate analysis using the Cox proportional hazards regression model identified lymphatic invasion as the only independent factor predicting local-regional recurrence (relative risk, 10.764; 95% confidence interval, 2.98 to 57.68). Our results suggest that the oncologic outcome of segmentectomy vs lobectomy is similar in this cohort of c-T1a N0 M0 NSCLC patients. These results will be validated by large-scale, prospective, randomized trials.