Postoperative respiratory failure is a serious problem in the anaesthetic management of patients with myasthenia gravis who undergo thymectomy. Although the classical recommendation is to avoid neuromuscular blockers, there is no strong evidence to support it. To evaluate the postoperative outcomes in patients with myasthenia gravis after thymectomy when anaesthetic management included rocuronium reversed with sugammadex. A retrospective cohort study. Nationwide acute in-patient care database. A total of 1143 patients with myasthenia gravis who underwent thymectomy were included. Data were collected from the medical insurance claims data of acute care in-patient hospitals. The postoperative complications when rocuronium reversed with sugammadex was compared against no muscle relaxant use using propensity score matching. The primary outcomes were the rates of in-hospital mortality, plasma exchange following thymectomy and the use of immunoglobulins. The secondary outcomes were the length of stay in the high dependency/ICUs, the total length of hospital stay and the duration and type of respiratory support following thymectomy. There were no significant differences between the propensity score matched groups in terms of plasma exchange [relative risk, 0.96; 95% confidence interval (CI), 0.64 to 1.43] and use of immunoglobulins (relative risk, 1.09; 95% CI, 0.60 to 1.97). The length of hospital stay was significantly shorter in patients in whom rocuronium and sugammadex were used: 29.0 vs. 35.4 days, P = 0.035. Anaesthetic management with rocuronium reversed by sugammadex was not associated with increased risk of respiratory complications. These findings could help in the anaesthetic management of patients with myasthenia gravis.