An intraoperative radiation therapy (IORT)-protocol was designed for poorly differentiated non-anaplastic thyroid carcinoma. Out of 155 cases of differentiated thyroid tumours, 12 showed marked vascular/capsular invasion. Five entered the study (three primarily local invasive tumours, two local recurring). IORT was administered after tumour surgery (4-10 GY) and combined with post-operative percutaneous irradiation. The tumour control rate in the thyroid bed was achieved in all five patients, 1/5 developed mediastinal nodes and 1/5 with primary mediastinal tumour extension showed tumour progression. No specific complications occurred.