OBJECTIVE To determine prognostic significance of lymphovascular invasion (LVI) in prostate cancer patients who underwent adjuvant or salvage postoperative radiotherapy (PORT) after radical prostatectomy (RP). METHODS A total of 168 patients with prostate cancer received PORT after RP, with a follow-up of ≥12 months. Biochemical failure after PORT was defined as prostate-specific antigen (PSA) ≥0.2 ng/mL after PORT or initiation of androgen deprivation therapy (ADT) for increasing PSA levels regardless of the value. We analyzed the clinical outcomes including survivals, failure patterns, and prognostic factors affecting the outcomes. RESULTS In total, 120 patients (71.4%) received salvage PORT after PSA levels were >0.2 ng/mL or owing to clinical failure. The 5-year biochemical failure-free survival (BCFFS), clinical failure-free survival (CFFS), distant metastasis-free survival (DMFS), overall survival, and cause-specific survival rates were 78.3%, 94.3%, 95.0%, 95.8%, and 97.3%, respectively, during a follow-up range of 12-157 months (median: 64 months) after PORT. On multivariate analysis, PSA level of ≤1.0 ng/mL at the time of receiving PORT predicted favorable BCFFS, CFFS, and DMFS. LVI predicted worse CFFS (p = 0.004) and DMFS (p = 0.015). Concurrent and/or adjuvant ADT resulted in favorable prognosis for BCFFS (p < 0.001) and CFFS (p = 0.017). CONCLUSIONS For patients with adverse pathologic findings, PORT should be initiated as early as possible after continence recovery after RP. Even after administering PORT, LVI was an unfavorable predictive factor, and further intensive adjuvant therapy should be considered for these patients.