Local recurrence in patients with thyroid carcinoma threatens speech, swallowing and the airway. IMRT is superior to standard radiotherapy for such concave targets. We report the first series of patients with thyroid cancer who were treated using IMRT. 36 thyroid cancer patients who were treated with IMRT from 2000 to 2003. 67% were post thyroidectomy for primary cancer, 33% were post resection of recurrent disease, most of which was in the tracheoesophageal groove (TE groove). 14% had gross residual tumor and 25% had microscopic positive margins. TNM stage was: T4-89% (invasion of prevertebral muscles14%, esophagus/hypopharynx 36%, trachea/larynx 42%, strap muscles 39%, skin 5%); N1-89% (mean 16 nodes positive, range 0–50), M1-33%. Histology was: 67% differentiated, 19% medullary; 11% anaplastic/undifferentiated; and 3% sarcoma. IMRT was used only for a boost in 12 cases. The 24 cases who had their entire volume and course delivered by IMRT were analyzed: CTV dose-volume statistics, normal tissues avoidance, toxicity, and outcome. 9 gantry angles were used (median, range: 7–11) and the prescribed dose was 84.5% of the maximum dose (mean, SD: 2.8%). CTV dose statistics are given in Table 1. CTVPrimary was prescribed 60Gy and encompassed the primary tumor bed, central compartment, adjacent level VI and IV nodes and supraclavicular fossa. CTVboost was prescribed 60-66Gy and encompassed regions of gross residual tumor or positive margins, usually around the TE groove. CTVNodal pos was prescribed 60Gy and encompassed regions which contained positive nodes and adjacent nodal level. CTVNodal neg was prescribed 54-57Gy and encompassed elective nodal levels beyond CTVNodal pos or contralateral nodes. CTVMediastinumwas prescribed 54-56Gy and encompassed superior mediastinal nodes. The maximum dose to spinal cord was 37.4Gy (mean, SD:6.4Gy), and the closest distance of the 45Gy isodose line to cord was 6.6mm (mean, SD:3.3mm). Volume of parotid irradiated to >24Gy was 39.1%, (mean, SD:22.2%) and mean dose was 21.6Gy, (mean, SD:8.1Gy). Volume of submandibular gland irradiated to > the prescribed 20-50Gy was 48.7% (mean, SD:23.1%) and mean gland dose was 31.2, (mean, SD:14.3Gy). Volume of lung irradiated to >20Gy was 24.9% (mean, SD:11.0%) and mean dose was 21.6Gy (mean, SD:8.1Gy). Volume of supraglottic larynx irradiated to > the prescribed 35–50 Gy was 45.0% (mean, SD: 17.1%) and mean dose was 41.9Gy (mean, SD: 8.3Gy). Most severe acute toxicity was grade 3 esophagitis/pharyngitis (62.5% incidence), grade 3 skin toxicity (29.2% incidence) and grade 3 mucositis (66.6% incidence). 29.2% of patients required tube feeding. Late toxicity were: Lhermittes syndrome (1 case), grade 1 pulmonary (1 case), grade 3 dysphagia (5 case), grade 1 xerostomia (4), grade 2 xerostomia (3 cases). At median follow 14.2 months (range 5.6- 35.8), only 1 patient failed adjacent to the CTV. His primary tumor was a T4N1 poorly differentiated tumor with invasion of esophagus and trachea. Recurrence was located in the contralateral TE groove which received <50Gy around a region contoured for avoidance of the cervical esophagus. 1 patient died of widespread metastases. Patients with locally aggressive thyroid cancer may present extensive target volumes. IMRT allows CTVs and doses to be sculpted to encompass the disease in primary tumor bed and central compartment, involved and adjacent elective nodes and superior mediastinum. The spinal cord, lungs, parotid and submandibular glands, supraglottic larynx, brainstem and brain should be outlined for avoidance. Lung volume irradiated to >20 Gy may exceed tolerance because of the multiple gantry angles employed. The lower larynx, cervical esophagus and TE grooves should be included within the target volume. Caution should be applied in avoiding normal tissues in this region.