Falls in the elderly are a major public health concern,because of devastating physical and psychological con-sequences among this population. A large proportionof falls in older adults occurs during daily activitiessuch as walking or stepping. These falls often resultfrom incorrect weight transfers (Robinovitch et al.2013), which could be associated with difficultiesexperienced by the elderly in controlling mediolateralstability (Rogers et al.2001).Initiation of stepping, which involves the transitionfrom a bipedal to a unipedal stance, constitutes a taskproviding a challenge for mediolateral dynamic stabil-ity. Indeed, the act of lifting the foot to execute thestep induces a reduction of the dimension of the baseof support, which results in a lateral fall of the whole-body toward the swing leg during the subsequent stepexecution. During volitional stepping, it is well knownthat this lateral instability is minimized by the anticipa-tory postural adjustments (APA) preceding the swingfoot-off. These APA are manifested by a lateral shift ofthe centre of pressure (CoP) toward the swing foot,which acts to propel the centre of mass (CoM) towardthe stance leg prior to swing foot, thereby attenuatingthe subsequent lateral CoM fall (Rogers et al.2001).The question of whether and how the mediolateralstability control during volitional gait initiation isinfluenced by the speed of progression has beenrecently addressed (Caderby et al.2014). It has beenreported that young individuals are able to finely tunethe temporo-spatial features of APA and the medio-lateral swing foot placement at heel-contact time so asto maintain mediolateral dynamic stability unchangedduring gait initiation whatever the gait speed (Caderby et al.2014). However, to date, it isunknown whether these findings are generalizable tothe elderly population.The aim of the present study was to examine theeffect of speed on mediolateral dynamic stability duringinitiation of stepping in older adults. We hypothesizedthat older adults would exhibit impairment in themediolateral dynamic stability when pace increases.