Background: Bilateral axillo-breast approach (BABA) robotic thyroidectomy has been successfully performed for thyroid cancer patients with excellent cosmetic results. Completion thyroidectomy is sometimes necessary after thyroid lobectomy, and whether it has a higher complication rate than the primary operation due to the presence of adhesions remains controversial. The aim of this study was to evaluate surgical outcomes, including operation time and postoperative complications, in patients who underwent BABA robotic completion thyroidectomy. Methods: From Jan 2012 to Aug 2020, 33 consecutive patients underwent BABA robotic completion thyroidectomy for a thyroid malignancy after BABA robotic thyroid lobectomy. The procedures were divided into five steps: (1) robot setting and surgical draping, (2) flap dissection, (3) robot docking, (4) thyroidectomy, and (5) closure. Clinicopathological characteristics, operation time, and postoperative complications were reviewed. Results: The total operation time was shorter for completion thyroidectomy than for the initial operation (164.8 ± 31.7 min vs. 179.8 ± 27.1 min, p = 0.043). Among the robotic thyroidectomy steps, the duration of the thyroidectomy step was shorter than that of the initial operation (69.6 ± 20.9 min vs. 83.0 ± 19.5 min, p = 0.009. One patient (1/33, 3.0%) needed hematoma evacuation under the flap area immediately after surgery. Three patients (3/33, 9.1%) showed transient hypoparathyroidism, and one patient (1/33, 3.0%) had permanent hypoparathyroidism. Two patients (2/33, 6.1%) showed transient vocal cord palsy and recovered within 3 months following the completion thyroidectomy. There were no cases of open conversion, tracheal injury, flap injury or wound infection. Conclusions: BABA robotic completion thyroidectomy could be performed safely without completion-related complication.