Traditionally it is recommended that hyperthyroid patients should be made euthyroid prior to thyroidectomy. However, several small observational studies have reported no increase in adverse events when hyperthyroid patients undergo thyroidectomy. The aim of this study was to assess outcomes following total thyroidectomy in patients who were biochemically hyperthyroid at the time of surgery compared to those who were euthyroid. One hundred and fifty-one eligible patients undergoing thyroidectomy for hyperthyroidism between January 2012 and February 2016 were identified, of whom 57 were hyperthyroid on perioperative blood tests and 94 were euthyroid (comparison group). Primary outcomes were 30-day mortality, increased length of postoperative hospital stay and intraoperative signs consistent with thyrotoxicosis (e.g. heart rate >100 per minute, systolic blood pressure >180 or <60 mmHg, or temperature >38°C). Secondary outcomes were intraoperative beta-blocker use and level of care required postoperatively. Thirty-day mortality was zero. The only significant difference between the two groups was a higher use of intraoperative beta-blockers amongst hyperthyroid patients (28.1% versus 8.5%, <i>P</i>=0.002). Our findings suggest that thyroidectomy for mild to moderate biochemical hyperthyroidism performed by an experienced thyroid surgeon and anaesthetist, is associated with increased intraoperative beta-blocker use but no statistical difference in mortality, length of postoperative stay or intraoperative signs consistent with thyrotoxicosis. While we still recommend attempting to achieve a euthyroid state whenever possible prior to thyroid surgery, mild to moderate degrees of residual biochemical hyperthyroidism when appropriately managed may not be associated with an increase in adverse outcomes.