Aims Half of head and neck cancer patients do not receive timely adjuvant radiotherapy (RT). We hypothesized that impaired post-operative (post-op) recovery measured by clinical grading and patient-reported outcomes (PRO) would predict delayed post-op RT in oral cavity cancer (OCC) patients with microvascular reconstruction. Methodology Single-tertiary-institution retrospective cohort study of OCC patients treated curatively from 2016-2021. Post-op modified barium swallow (MBS) identified anastomotic leaks; oral and pharyngeal swallow function was graded with MBS Impairment Profile (MBSImP) oral efficiency component, and Dynamic Imaging Grade of Swallowing Toxicity (DIGEST) scales. MDADI (MD Anderson Dysphagia Inventory) scores reflected patient reported swallow-related quality of life (QoL). Logistic regression identified factors associated with delayed RT initiation (>6 weeks post-op). Results 72 patients (median age 61.0 years [IQR: 53.2-65.8], 59.7% male, 90.3% advanced AJCC VIII stage) were included. Median surgery-to-RT interval was 6.3 weeks (IQR: 5.4-7.2); 51.4% initiated RT >6 weeks post-op. Clinicopathologic characteristics did not differ between timely (≤6 weeks) and delayed (>6 weeks) groups. Overall survival (OS) was comparable (3-year OS: 82.2% vs 69.5%; log rank p=0.60). Rates of post-op anastomotic leak did not differ between both groups (2.9% vs 13.5%, p=0.227). On univariable analysis, MDADI functional score (MDADI-f) in the lowest quartile was associated with higher odds of RT delay (OR 3.05, 95% CI:1.06-8.74, p=0.038). Other MDADI subscales, MBSImP, DIGEST grade, gastrostomy, stage, and age were not significant. On multivariable analysis adjusting for age and stage, MDADI-f in the lowest quartile remained independently associated with RT delay (OR 2.92, 95% CI:1.01-8.46, p=0.049). Conclusion Poor post-op swallow-related QoL independently predicts delayed adjuvant RT. The role of PROs in timely adjuvant RT merits further investigation.