Despite the fact that the pathologic changes of the foot in rheumatoid arthritis are quite specific and common, studies on statistics and pathomechanism of rheumatoid foot are relatively rare. In view of this, clinical and X-ray studies as well as study on pathomechanism of deformation of foot were carried out with 103 patients of rheumatoid foot (182 foot) that visited the outpatient ward of Orthopaedic Surgery of Okayama University for the period covering from January 1963 to March 1964. The results are in the following. It has been found that the rheumatoid patients having pathologic changes of the foot amounted to 56% , showing the incidence to be higher than what is generally thought. It is to be noted that the sites where pathologic change of ankle joint proved to be most severe are the anterior and posterior regions of medial and lateral malleolus, followed by Chopart's joint, and these proved to be the main factors for talipes planovalgus. Rep esentative deformations of the rheumatoid foot are eversion of heel, talipes planus, hallux valgus, and hammer toe. The onset mechanism of these deformations may be explained as to start with inflammation of synovial membrane due to rheumatism, which is followed by the weakening of ligaments and muscles constituting the joint capsule and the joint, then the subsequent accumulation of static and kinesiologic factor makes the pathologic deformation definitive. Differences between rheumatoid hand and rheumatoid foot are not only limited to local inflammation and anatomical elements, but also to the foot there arises an additional problem of weight bearing. With respect to functional disturbances in the case of a rheumatoid foot main complaints are less in spite of the injury of bone and deformation. when the comparison is made between Europeans and Americans on one hand and Japanese on the other, differences in the modes of living have a telling influence, and of Japanese people with rheumatoid feet they may experience some inconvenience in their routines of life but they are not so much bothered by their functional disturbance.