We performed a retrospective record review of patients who received large lobar remnant ablation after surgery for well-differentiated thyroid carcinoma including 30 with papillary carcinoma, 14 with follicular carcinoma, and 6 with Hürthle cell carcinoma. We compared these 50 patients to a group of patients who underwent total or near-total thyroidectomy for well-differentiated thyroid carcinoma. The ablation group was treated with single outpatient doses of 29.9 mCi (131)I to prepare for whole-body radioiodine scanning. Subsequent serum thyrotropin (TSH) concentration during thyroid hormone withdrawal was greater than 25 microU/mL in 94% of patients. The mean TSH in this population (76 microU/mL) was not statistically different from a group of 50 patients who underwent total or near-total thyroidectomy (mean, TSH 71 microU/ml p = 0.84). Twenty-four hour radioiodine uptake post-29.9 mCi (131)I ablation was less than 1% in 80% of patients. The mean radioiodine uptake (0.8%) in the lobe ablation population was significantly lower than in patients treated with total thyroidectomy (mean, 2.4%, p < 0.001). There was minimal morbidity after 29.9 mCi (131)I ablation of large lobar remnants. Outpatient 29.9 mCi (131)I ablation is a safe, effective, and less costly alternative to completion thyroidectomy in selected patients. Although we included patients with both papillary and follicular carcinoma in our review, we recommend this method for patients with minimally invasive follicular carcinoma requiring whole body scanning, even with large postsurgical remnants in place.