Abstract: A 36-year-old woman with Graves’ disease underwent thyroid ablation with oral 131I (20 mCi) following poor control of hyperthyroidism with carbimazole. Three days later, she presented to the emergency department with a choking sensation, shortness of breath, dysphagia, neck discomfort, and swelling. The prevertebral soft tissue was grossly thickened on the lateral neck radiograph. An urgent contrast-enhanced CT neck revealed severe neck edema and thyroiditis. TSH and free T4 levels were normal, and the neck swelling gradually resolved with corticosteroids. Acute neck edema is an infrequent complication of 131I ablation, and cross-sectional imaging is useful to exclude airway compromise or infection.