In this study, we have tried to clarify the role of rheumatoid lesions of the tendons and adjacent soft tissues in the development of finger deformities. Other factors, such as loss of cartilage and bone substance, rheumatoid pannus formation, growth (in children), shrinkage as a result of scarring, bone fusion, way of using the hand, and pain, may also contribute to the development of the deformation. The most important factor, however, is the changes which occur in the tendons and related structures, especially in the early stages. The primary factor seems to be the inflammatory softening and distension of the joint capsule. This is followed by loss of power in those muscles which are attached to the capsule, as a result of which the antagonistic muscles may pull the joint into a deformed position without causing any associated spasm. The type of deformity that results seems to be primarily determined by the anatomical conditions of the hand and the type of inflammation.