From early on in the domestication history of horses, their relation to humans has been largely centered around a working relation through harnessing and riding. Archeological data trying to estimate when riding first occurred are largely based on examination of teeth and spine, both showing traces of bit actions and rider's weight on the back respectively. Thus, work does affect the horse's body but the question remains of whether this is so that horses' welfare may be altered both during the working sessions and/or in a more chronic way, with consequences outside the working sessions. In this presentation, we will review the existing evidence of the potential effect of work on the overall welfare of horses and try and identify the behavioural indicators of discomfort at work as well as the indicators of work related problems outside the working situation. Studies converge to show that increased emotionality, behavioural disorders and aggressiveness outside work may in some cases result from the type of work the horses are used for or the way it is performed. Different approaches lead to a high prevalence of back disorders in sport horses that could explain for some part some of these welfare problems. We will try and disentangle the potential mechanisms relating welfare issues to work in horses and propose manageable solutions of improvement that would not only avoid altering horses 'well being but also may lead horses to enjoy working, as seen in certain facilities.