Abstract: The physical as well as the behavioural requirements of the horse changed little through the process of domestication. This means that horses kept within an intensively housed environment and used for performance, physically and behaviourally are susceptible to specific clinical conditions, injuries and diseases. In this chapter, physiological and clinical problems such as those causing pain related behaviours and head shaking are discussed. The most commonly associated problems with horses kept in intensive housing conditions or used in specific competitive disciplines are highlighted. Despite the increasing amount of information about injury and disease in the horse, there is little research relating such problems to the situations performance horses have to cope with. This is particularly the case with pain, whose recognition of pain amongst professionals is still variable and often subjective and not widely recognised as a cause of behavioural change.