High control performance i essential in manu precision positioning applications, such as control of the vertical sample position in a atomic-force microscope (AFM). This paper investigates the impact of load flexibility on piexoelectrically actuated positioning systems in terms of control performance. The modeling method used combines model analysis with simple transfer function manipulations, and shows, how the load dynamics may influence the ocntrol performance. The analysis is experimentally verified on a commercial AFM system.@en