Objective: Well-differentiated thyroid carcinoma is considered an indolent malignant disease. Although rare, extrathyroidal invasion is associated with a worse prognosis and increased risk of morbidity. Management remains controversial, with some authors advocating conservative treatment with preservation of midline structures and others, aggressive extensive en bloc resection. The aim of this study was to report our 40-year experience with invasive thyroid carcinoma, with emphasis on the clinical characteristics and the effect of different treatment modalities on survival. Study design and setting: A retrospective study including a file review of 1,200 patients with a diagnosis of well-differentiated thyroid carcinoma of whom 49 (5%) showed involvement of an adjacent structure (larynx, trachea and esophagus) (study group). Type of surgery, radiation treatment, radioiodine treatment, and patient demographics were evaluated. Results: Compared to the rest of the patients, the study group was characterized by a higher rate of male patients (39% vs 25%), and older average age (58 vs 45 years). Average size of the primary tumor was 3.7 cm. Sixteen patients underwent radical surgery and 33 conservative surgery followed by radioiodine treatment. Five-year survival and recurrence rates for the whole group were 78% and 52%, respectively. The only statistically significant factor for survival was large tumor size. Distant metastases developed in 46% of patients, all in the lungs. Ten of 14 deaths were due to distant metastases. External radiation, used in 52% of the patients, was associated with worse prognosis. Conclusion: Conservative procedures followed by radioiodine treatment are associated with similar survival rates as aggressive techniques, with less perioperative mortality and lower overall morbidity. Significance: This study provides further evidence that in cases of invasive thyroid tumors the extent of the primary surgery seems to have no influence on survival. EBM rating: C-4.