The aim of this study was to investigate the therapeutic outcome and prognostic factors in 36 patients with resectable thymoma who were referred to our clinic following surgical resection. The median age was 45 years, ranging from 19 to 72 years. Myastenia gravis was observed in 28 patients (77.7%). The most frequent histologic subtype was epithelial (n = 21, 58.3%), followed by the lymphocytic type (n = 6, 16.7%). Stage at presentation was distributed as stage 1, 2 patients (2.7%); stage 2, 19 patients (52.8%); stage 3, 10 (27.8%); and stage 4, 3 patients (8.3%). The majority of the patients (n = 32, 88.9%) had completely resectable disease, whereas 2 patients had microscopic and 2 more patients had macroscopic residual disease after surgery. Adjuvant radiotherapy was administered to 28 patients. After a median follow-up period of 39 months, 5 patients (16.1%) experienced recurrence. There was a significant negative correlation between recurrence and adjuvant radiation therapy (two-sided p = 0.0001). There were no objective responses to chemotherapy given to 4 patients for recurrent disease. Overall survival (OS) and progression-free survival (PFS) was 82.8% and 76.6% at 5 years, respectively. Adjuvant radiotherapy had a significant association with both OS (p = 0.039) and PFS (p = 0.00001). Furthermore, recurrent disease was observed to have a significant negative impact on OS (p = 0.039). The results of this study suggest that adjuvant radiotherapy may provide survival benefit in patients with resectable thymoma, regardless of surgical margins.