Our interest in valvotomy for mitral stenosis extends back over several years, although it was not until September, 1948, that our first patient was operated on. In June, 1950, we were able to report our experiences in nine patients, seven with successful operations (Baker, Brock, and Campbell, 1950). We are now able to report the immediate results on 100 patients treated by operation, with a more detailed analysis and follow-up of the first 50, the last of whom was operated upon in May, 1951, so that all have been followed for six months, the majority for more than a year, and some for two to three years. Apart from two patients at the Johns Hopkins Hospital, Baltimore, the operations were done at either Guy's Hospital or the Brompton Hospital, and all by one surgeon. For the purpose of analysis and follow-up the two Baltimore cases have been omitted from the first 50. In previous papers we have followed common usage in writing of pulmonary or mitral " valvulotomy," but it is a valve and not a valvule that is divided, and we think the term " valvotomy " is more correct, even though it is still a hybrid formation. The operation really does more than splitting the commissures, for if the valve cusps are reasonably supple the operation may enable them to close better and more normally, but we have thought it better to reserve the term " valvoplasty " for more elaborate operations that may be possible in the future.