Patients with ankylosing spondylitis (AS) may experience a progressive spinal kyphosis, which induces a forward and downward displacement of the centre of mass (COM) of the trunk with consequent use of mechanisms to compensate for the displacement of the trunk. The analysis of patterns of movement gives an important opportunity for follow-up of patients and is an useful tool to plan a therapeutic and rehabilitative program. Objective: The aim of our study was to contribute to the description of abnormalities of gait biomechanics in patients with AS and to individualize, if existing, a typical pattern of these patients. Methods: Five patients with AS (3 men, 2 women) were evaluated by gait analysis. Each patient was assessed with dynamic electromyography, with survey of phases of gait cycle and 3D video-analysis of gait related to data of platform (Digivec ®) which allows to display real time the force vector of reaction foot-ground overlapping the screen image of patient. Results: The dynamometric platform located the following problems: increasing of the medium-lateral component of the reaction force on the ground in the mild and terminal stance. The anterior-posterior reaction force is diminished in both the initial and the terminal component. The timing of activation of the tibialis anterior results prolonged while the timing of activation of the gastrocnemius medialis results delayed. Conclusion: The patients with AS prefer therefore an eccentric contraction of the tibial anterior in comparison to a concentric contraction of the gastrocnemius medialis, “opting” for a gait strategy that confers greater stability but limited power.