Background: With the increasing number of patients performing mitral valve replacement for many pathologies such as rheumatic or degenerative valve, reoperation for prosthetic mechanical valve dysfunction became more frequent. The aim of this work is to collect, review and analyze the data of patients with prosthetic mitral valve thrombosis or malfunction and evaluate the different variants that can affect the outcome of surgical intervention in these patients. Method: Our study included 40 patients with prosthetic mitral valve thrombosis or malfunction, who underwent re-replacement of mitral valve prosthesis over 20 months (from the first of November 2013 till the end of June 2015) in Kasr Al-Ainy University Hospitals. Preoperative, operative, and postoperative data were collected and analyzed prospectively and evaluated for risk factors affecting hospital mortality and morbidity. Results: Our patients were 11 males (27.5%) and 29 females (72.5%). The age was ranged between 20 - 73 years with a mean of 35.8 ± 10.1 years. The overall mortality was 7 of the 40 patients (17.5%). The main risk factors for hospital mortality were preoperative mean arterial blood pressure < 70 mmHg, heart rate > 100 /minutes, acute pulmonary edema, need for preoperative mechanical ventilation, cerebrovascular stroke, disturbed conscious level, preoperative renal dysfunction and low EF. Also, mortality was significantly positively correlated with long cross clamp time, long cardiopulmonary bypass time, need for high inotropic support after weaning from bypass, postoperative mechanical ventilation time, renal failure, stroke, chest infection and wound infection. Conclusion: Hemodynamic instability, low EF, renal dysfunction and long operative time were especially associated with increased mortality. Earlier surgical management before the development of severe heart failure and myocardial dysfunction would improve the results of redo mitral valve surgery.