The objective of this study is to characterize postoperative myasthenic crisis (POMC), after extended thymectomy and discuss the treatment options for this condition. Clinical data from patients with generalized myasthenia gravis (MG) who underwent extended thymectomy at Xuanwu Hospital of the Capital Medical University from 2016 to 2018 were reviewed retrospectively. Patients were divided into two groups-POMC and non-POMC. Variables that could potentially predict POMC were analyzed. In the POMC group, the aforementioned variables were compared between patients with and without pneumonia. Ninety-seven patients were enrolled. Thirty-eight (39.2%) patients developed POMC. The mean duration of mechanical ventilation (MV), length of intensive care unit stay, and duration of hospital stay were significantly longer in the POMC group (P < 0.001). Multivariate logistic regression analysis showed that disease severity, symptom duration longer than 12 mo, and transsternal thymectomy were independent risk factors for POMC. Postoperative pneumonia significantly prolonged the MV period (P = 0.012) and weaning from MV after intravenous immunoglobin (IVIg) treatment (P = 0.005) in POMC patients. Twenty-four (24.7%) POMC patients who received IVIg were successfully weaned from MV and were discharged. Disease severity, symptom duration longer than 12 mo, and transsternal thymectomy were independent risk factors for POMC. Postoperative pneumonia worsens the prognosis of POMC. Copyright © 2020 Elsevier Inc. All rights reserved.