the objective of our study was to clarify survival and treatments in patients with incompletely resected thymoma. between January 1991 and December 2012, 156 consecutive patients who underwent thymectomy with curative intent at Kyoto University Hospital, were evaluated retrospectively. Overall survival and progression-free survival were analyzed using the Kaplan-Meier method, comparing the complete resection group (n = 141) with the incomplete resection group (n = 15). Potentially relevant factors for overall survival and progression-free survival in patients with incompletely resected thymomas were analyzed using Cox proportional-hazard models. there was a significant difference in progression-free survival (p = 0.0012) but not in overall survival (p = 0.638) following thymectomy in the complete and incomplete resection groups. Adjuvant chemotherapy was performed in 6 (40%) patients and adjuvant radiotherapy in 6 (40%) in the incomplete resection group. In univariate analysis, younger age (p = 0.073) showed a tendency for better overall survival, and adjuvant chemotherapy (p = 0.071) showed a tendency for better progression-free survival. our results suggest that patients with incompletely resected thymomas can achieve comparable overall survival to those with completely resected thymomas. Adjuvant chemotherapy for incompletely resected thymomas tends to improve progression-free survival.