PURPOSE: Most patients with tongue cancer require surgical resection of the tongue to varying degrees. As a result, quality of life, which is strongly related to speech, chewing, and swallowing, can deteriorate severely from extensive surgical treatment of tongue cancer. In addition to surgery, adjuvant therapy may affect the severity of functional impairment. Therefore, the influence of postoperative radiotherapy on functional outcome after partial glossectomy with free flap reconstruction was evaluated in patients with early oral tongue cancer. PATIENTS AND METHODS: Functional outcome was measured and charts of 31 patients with oral tongue cancer who were surgically treated at Yonsei Head and Neck Cancer Clinic from 2003 through 2008 were reviewed. Only patients who underwent partial glossectomy and reconstruction with radial forearm free flap and did not develop recurrence were included. Speech integrity was evaluated with diadochokinetic testing by a professional speech therapist. Tongue mobility was checked by measurements of upward distance, protrusion distance, and lateral deviation distance. Swallowing capacity was evaluated with the M.D. Anderson Dysphagia Inventory. RESULTS: Diadochokinetic rates of the surgery-only and postoperative radiotherapy groups were 27.8 and 23.9, respectively, which was statistically different. Swallowing capacity was significantly superior in the surgery-only group. Tongue mobility was not statistically different between the 2 groups. CONCLUSIONS: Functional outcome of speech and swallowing is negatively influenced by postoperative radiotherapy.