BACKGROUND Radiotherapy is used commonly in the treatment of patients with head and neck carcinoma. The benchmark radiotherapy utilization rates for head and neck carcinoma largely are unknown. The objective of the current study was to determine the optimal radiotherapy utilization rate for patients with head and neck carcinoma and to compare this optimal rate with actual utilization rates where actual utilization data were available. METHODS An optimal radiotherapy utilization tree was constructed that depicted all patients with head and neck carcinoma in whom radiotherapy was indicated according to evidence-based treatment guidelines. The proportions of patients with clinical attributes that indicated possible benefit from radiotherapy were obtained from epidemiological data and were inserted into the utilization tree. The optimal proportion of patients with carcinoma of the head and neck who should receive radiotherapy was calculated by merging the evidence-based recommendations with the epidemiological data in the tree. Optimal rates of radiotherapy utilization were compared with actual rates obtained from population-based studies. RESULTS Radiotherapy was indicated at some point during their illness in 74% of all patients with head and neck carcinoma. By subsite, the optimal radiotherapy utilization rates were oral cavity, 74%; lip, 20%; larynx, 100%; oropharynx, 100%; salivary gland, 87%; hypopharynx, 100%; nasopharynx, 100%; paranasal sinuses, 100%; and unknown squamous cell carcinoma of the head and neck, 90%. All treatment recommendations were based on Level III or IV evidence. Assessment of actual radiotherapy utilization rates indicated an increased use of radiotherapy over time for head and neck carcinoma. However, there also were some decreases in the use of radiotherapy for some carcinoma subsites over the past 20 years, despite the lower actual rates compared with the optimal rates. The reasons for these reductions in use were not identified. CONCLUSIONS The actual radiotherapy utilization rate for patients with head and neck carcinoma corresponded reasonably closely to the optimal rate for some populations but also identified some shortfalls for other patient groups. The results of this study provide a way of assessing shortfalls in radiotherapy.