AbstractBipedal human motion is related to the original shape of the foot. Distortion and degenerative changes may be caused by failure in the complex chain of movements. There are few references to valgus flatfoot in either the palaeopathological or medical literature. The study of three French medieval series (Macon, Larina and Cutry) in the osteological collections of the CEPAM (UMR 6130 – CNRS/UNSA) at Valbonne (France) enabled us to define several significant osseous signs which provide evidence of abnormal biomechanical constraints following structural change in the foot. The consequences of the change of axis of the talar pulley, abnormal osseous contacts, and evolutionary modifications noticed in some synostoses of the tarsus, are particularly useful for study. Analysis of the location of arthritic change in the joint may produce an additional coherent argument to the diagnosis. The recognition of flatfootedness in an archaeological context provides a marker of health and of distress, which is all the more interesting since bones required for this diagnosis are often present and relatively well preserved in the excavations of burials. Copyright © 2006 John Wiley & Sons, Ltd.