Well-differentiated thyroid carcinoma infrequently invades the upper aerodigestive tract. However, when invasion occurs, it is the source of significant morbidity. The most common structures invaded by thyroid carcinoma are the recurrent laryngeal nerves, larynx, pharynx, and esophagus. Invasion of these structures produces symptoms of airway insufficiency, dysphagia, and hemoptysis. This study was designed to define more clearly the significance of invasion of papillary thyroid carcinoma on survival. At the Mayo Clinic, 262 patients treated for invasive papillary thyroid carcinoma between 1940 and 1990 were retrospectively evaluated. In this group the sites of invasion were muscle 53%, trachea 37%, laryngeal nerve 47%, esophagus 21%, larynx 12%, and other sites 30%. Complete tumor removal was accomplished in 56% of cases. Kaplan-Meier survival curves were calculated for the population. The overall survival was 79% at 5 years, 63% at 10 years, and 54% at 15 years. When the Cox proportional hazard model was applied to the survival data, the factors that had significant influence on survival were invasion of the trachea and the esophagus. Completeness of resection approached statistical significance. Muscle invasion, laryngeal invasion, and recurrent laryngeal nerve invasion had no significant independent influence on survival. These data suggest that when papillary thyroid carcinoma extends beyond the thyroid capsule and invades adjacent structures, the site invaded will influence survival. Survival may be improved in those cases in which complete surgical excision of the tumor is performed.