In order to find out the long-term results of mitral valvotomy as a closed heart operation, the authors investigated the fate of patients who underwent surgery twenty years ago. In 1955, 148 mitral valvotomies by the closed technique were carried out in the Cardiovascular Department of the Broussais Hospital under the direction of Professor F. D'Allaines. There were 15 operative deaths (10 p. 100) and 12 late deaths of non-cardiac origin; only 55 of the patients could be traced for follow-up. After 20 years, 24 of them had still a good or moderate result, and 34 had a bad result. A study of the various characteristic features of the heart defect before operation, and of the operative findings, has allowed us to determine a certain number of factors which presage good immediate and long-term results. The authors have concluded that, if these factors are present, mitral valvotomy as a close technique, with its advantages of simplicity and economy, remains a perfectly valid operation.