Thyroid stunning has been reported as the temporary impairment of thyroid tissue after a 111-MBq or greater diagnostic 131I dose that decreases the final absorbed dose in ablative therapy. Concerns regarding the reality of stunning have arisen in part due to a flawed study design in prior reports. To assess whether a stunning effect has any impact on therapeutic outcomes, we compared initial treatment ablation rates in patients who received 111- to 185-MBq 131I diagnostic scans (n = 37) before ablative doses of 3700-7400 MBq with ablation rates in patients who did not receive any 131I before the initial treatment dose (n = 63). Ablation rates were 64.9% for scanned patients and 66.7% for nonscanned patients, a nonsignificant difference. Nonscanned patients with metastatic lesions (n = 23) were ablated at a higher rate (78.3%) than scanned patients (n = 9) (66.7%), but the difference was not significant (P = 0.50). It is possible that the reported stunning phenomenon, specifically its impact in temporarily impairing tissue, has been overemphasized.