Hippotherapy is a method of treatment used by physiotherapists, which involves horses as treatment tools. Kinematic analyses of the horse's back are usually carried out on a treadmill. However, for the requirements of hippotherapy, an assessment of the movement in overground conditions is necessary. This study investigates the relationship between the walking speed of the horse and the vertical and horizontal displacements of chosen points on the horse's back. Our hypothesis is that the vertical and horizontal displacements of the equine back are influenced by the speed of the movement of the horse when walking. 7 horses (age 13.1 +/- 2.6 years) took part in the study. Hemispheric markers were attached to selected points on the horse's back (top of the withers, a point at a quarter distance from the top of the withers to the sacral tuber, a point halfway between the distance from the top of the withers to the sacral tuber, the sacral tuber, the left and right proximal scapular spine, and the left and right coxal tuber) and were tracked semi-automatically while walking at 3 different speeds of movement (slow: 1.07 +/- 0.08 m.s(-1), regular: 1.38 +/- 0.09 m.s(-1), fast: 1.59 +/- 0.13 m.s(-1)). The range of movement of the selected points in the vertical and laterolateral directions was determined and evaluated in relation to the speed of the movement. Data were statistically analysed using the Friedman test and sign test. With increasing speed, there is an increase of both the stride length and stride frequency. In the central part of the back and at the pelvic end, the increasing walking speed led to an increase in vertical and, in the case of the pelvic area, horizontal (laterolateral) displacement. In the thoracic area there was a tendency towards a decrease in lateromotion and an increase in axial rotation with increasing speed. The length of the step, the vertical displacement of the pelvic parts of the back and the stride frequency were greater during the fast walk in comparison with the slow walk. This is of clinical relevance, as substantial movement of the pelvic part of the back can influence the patients during hippotherapy in the cases when they are lying on their stomach, with their elbows in the region of the coxal tuber of the horse's back.