A 62-year-old woman with severe mitral stenosis and two large parietal thrombi inside the left atrium is described. The patient was admitted to the hospital because of heart failure. Transthoracic and transesophageal echocardiography showed a severe calcific mitral stenosis and two large (56.9 and 46.2 mm in diameter) parietal thrombi inside the left atrium attached to the interatrial septum and associated with severe spontaneous echo contrast. This severe spontaneous echo contrast was detected in the left atrium and in the left atrial appendage. The patient was referred for cardiac surgery. The two large parietal thrombi were removed, and the valve was replaced with a Sorin-Bicarbon mitral valve prosthesis. Intraoperative transesophageal echocardiography after replacement of the mitral valve prosthesis and removal of the thrombotic mass showed absence of any spontaneous echo contrast in the left atrium and in the left atrial appendage. This report describes the diagnostic approach and successful surgical treatment of two very large parietal thrombi inside the left atrium associated with severe mitral stenosis and atrial fibrillation, which is a rare occurrence.