Purpose: The purpose of this retrospective study is to present the results of postoperative adjuvant radiotherapy after primary surgery for squamous cell carcinoma of the tongue base and to compare these results to those obtained with surgery alone. Methods: Between 1974 and 1993, continuous-course postoperative radiotherapy was delivered to 24 patients (Adjuvant Radiotherapy Group). Results were compared to those from a group of 55 patients treated with surgery alone (Surgery Group). Results: Characteristics of the two groups were similar, except that a larger proportion of patients in the Adjuvant Radiotherapy Group had higher pathologic TNM stages. Ipsilateral neck control (87% vs. 68%, p = 0.04), contralateral neck control (100% vs. 76%, p = 0.002), relapse-free survival (64% vs. 46%, p = 0.04), and control above the clavicles (80% vs. 48%, p = 0.007) were significantly higher in the Adjuvant Radiotherapy Group compared to those in the Surgery Group (5-year figures shown). Conclusion: The use of adjuvant radiotherapy after surgical resection of tongue base squamous cell carcinoma significantly decreased the rate of local-regional recurrence and improved relapse-free survival compared with surgery alone but did not alter cause-specific or overall survival.