Background <p>The prognostic significance of perineural invasion (PNI) and lymphovascular invasion (LVI) in early-stage oral squamous cell carcinoma (OSCC) remains uncertain. The role of postoperative radiotherapy (PORT) in this subgroup is debated. This study aimed to clarify the clinical impact of PNI/LVI and determine the effect of PORT across risk-stratified subsets of early-stage OSCC.</p> Methods <p>We retrospectively analyzed 6,121 patients with <i>p</i>T1-2N0M0 OSCC from the Taiwan Cancer Registry (2018–2022). Patients were categorized into Group A (PNI–/LVI–) and Group B (PNI+ and/or LVI+). Clinicopathological characteristics, survival outcomes, and the effect of PORT were assessed using multivariable analysis and propensity score matching (PSM).</p> Results <p>The PNI/LVI positivity occurred in 13.5% of patients and was independently associated with poorer differentiation, greater depth of invasion (&gt; 5&#xa0;mm), T2 classification, tongue subsite, lower BMI, and female sex. Group B patients exhibited significantly lower overall survival (HR 1.45, <i>p </i>= 0.001) and disease-free survival (HR 1.44, <i>p </i>&lt; 0.001), with inferior locoregional control versus Group A. PORT significantly improved locoregional control in Group B (<i>p </i>= 0.005), but no overall or disease-free survival benefit was observed, likely due to effective salvage surgery. In contrast, in Group A, PORT offered no benefit and was associated with worse outcomes.</p> Conclusions <p>Perineural invasion and/or LVI represent key adverse prognosticators in early-stage OSCC. Postoperative radiotherapy selectively enhances locoregional control in intermediate-risk patients, but survival outcomes remain unaffected. A risk-adapted therapeutic approach is warranted, tailoring PORT to patients with adverse features and avoiding overtreatment in low-risk cases.</p>