The authors have reviewed their experience with interstitial brachytherapy for the base of tongue cancer with the purpose of introducing treatment strategy and technique and presenting results. Between January 1993 and May 1999 twenty-one patients with primary squamous cell cancer of the base of tongue (T1-4N0-2) were treated by interstitial radiotherapy (RT). Seventeen patients with advanced stage cancer received brachytherapy (BT) boost after 60-66 Gy teletherapy and 4 patients with early stage (T1-2N0) were managed by sole BT after tumor excision and elective neck node dissection in case of positive or very narrow (< 5 mm) margin. High-dose rate (HDR) after-loading unit (Ir-192 source) was used with rigid needles or flexible plastic tubes. The treatment plan was performed by PLATO 3D BT planning system. The mean dose of boost BT or sole BT was 20 Gy (12-24 Gy) and 27 Gy (24-30 Gy), respectively. All treatments were delivered on consecutive days with a twice daily fractionation schedule, except the rigid needle technique (n = 4), where the dose was 12 Gy with a single fraction. After definitive RT of advanced stage disease, the rate of complete or partial remission was 65% (11/17) and 35% (6/17), respectively. At a mean follow-up time of 32 months the local tumor control for the entire patient population was 62% (13/ 21). Five patients (24%) died of local and/or regional failure and sixteen patients (76%) are alive (6 with local and/or regional disease and 10 without evidence of disease). All of the four sole BT treated patients belong to the latter group. The incidence of grade 2 or grade 3 mucositis was 48% and 52%, respectively. To achieve good local control with adequate doses, avoiding surgical morbidity and associated functional loss and to minimize late radiation sequelae, the combination of percutan and interstitial RT seems to be very advantageous in the treatment of the advanced tumor of the base of tongue. For patients with early stage (T1-2N0) cancer, sole postoperative BT of the tumor bed - by positive or very narrow margins - seems to be a feasible option. However, more patients and longer follow-up is required to define the value of sole BT.