OBJECTIVES Thymectomy plays an important role in the comprehensive treatment of myasthenia gravis. The present study aimed to investigate the risk factors for postoperative myasthenic crisis (POMC) in these patients and then establish a predicting model based on preoperatively available indicators.METHODS The clinical records of 177 consecutive patients with myasthenia gravis who received extended thymectomy between January 2018 and September 2022 in our department were retrospectively reviewed. Patients were divided into 2 groups according to whether they developed POMC. Univariate and multivariate regression analyses were conducted to identify the independent risk factors of POMC. Then a nomogram was constructed to intuitively show the results. Finally, the calibration curve and bootstrap resampling were used to evaluate its performance.RESULTS POMC occurred in 42 (23.7%) patients. By multivariate analysis, body mass index (P = 0.029), Osserman classification (P = 0.015), percentage of predicted forced vital capacity (pred%) (P = 0.044), percentage of predicted forced expiratory volume in the first second (pred%) (P = 0.043) and albumin to globulin ratio (P = 0.009) were identified as independent risk factors and entered into the nomogram. The calibration curve showed good concordance between the predicted and actual probability of prolonged ventilation.CONCLUSIONS Our model is a valuable tool for predicting POMC in myasthenia gravis patients. For those high-risk patients, appropriate preoperative treatment is necessary to improve the symptoms and greater attention to postoperative complications is needed.