Twenty-three-hour observation or "same-day" thyroid surgery was initiated at our institution for patients with nodular thyroid disease in July 1993. A retrospective review of all patients with nodular thyroid disease who underwent same-day thyroid surgery was performed to determine the safety and cost effectiveness of this approach. Eighty consecutive patients with nodular thyroid disease underwent thyroidectomy, followed by < or = 23 hours of observation in 71 (88%) and a planned hospital admission in 9 (12%) patients. Hospital admission preceded thyroidectomy in four patients (5%) because of transient ischemic attacks (one), airway obstruction (one), pulmonary disease (one), and suppurative thyroiditis (one). Five patients (6%) had a planned postoperative admission because of concominant modified neck dissection (two), median sternotomy (two), or soft tissue tumor resection (one). Of the 71 patients who underwent same-day thyroid surgery, 47 had near-total or total thyroidectomy, 20 lobectomy, and 4 completion thyroidectomy. Morbidity consisted of hematoma in one, recurrent laryngeal nerve paresis in two, and transient hypocalcemia in eight patients. Only 1 of the 71 patients required subsequent hospitalization for an anxiety attack. There was no mortality. Twenty-three-hour observation was associated with a 32 per cent and a 47 to 56 per cent reduction in cost for unilateral and bilateral thyroidectomy, respectively. Same-day thyroid surgery is a safe and costeffective approach for patients with nodular thyroid disease.