Abstract Background A control chart can help to interpret and reduce sources of variability in patient safety by continuously monitoring indicators. The aim of this study was to monitor the outcome of thyroid surgery using control charts. Methods Patients who had thyroid surgery during 2006–2007 were included in the study. Safety was monitored based on postoperative complications of recurrent laryngeal nerve palsy and hypocalcaemia. Indicators were extracted prospectively from the hospital information system and plotted each month on a P-control chart. Performance of the surgical team was also measured retrospectively for 2004–2005 (baseline period) to compare surgical outcomes before and after control chart implementation. Electromyographic monitoring of recurrent laryngeal nerves was not used, nor was calcium or vitamin D given routinely. Results The outcomes of 1114 thyroid procedures were monitored. Although the proportion of patients with recurrent laryngeal nerve palsy was similar for baseline and monitored periods (6·4 and 7·2 per cent respectively), there was a 35·3 per cent decrease in hypocalcaemia after implementation of control charts (P < 0·001). Complications almost doubled during a period when one surgeon was away and operating room renovations took place. Conclusion Outcome monitoring in thyroid surgery using control charts is useful for identifying potential issues in patient safety.