The method of biopsying biological tissue is an established procedure of minimally invasive medicine to extract samples for the determination of the presence or extent of a disease. Therefore punch biopsy is the most frequently applied method in case of prostate or breast cancer. The biopsy system is monitored during the penetration process into tissue via sonography. These observations of the procedure showed a considerable deflection of the needle tip. It is caused by unbalanced forces acting on the tip and by the low bending stiffness of the system itself. Government financed experimental studies using realistic phantom tissue have been conducted to quantify the needle deflection and to develop a mathematical approach to simulate this effect. This simulation has used a combination of a deformable model of the biopsy system in combination with a parameterized tissue model in multibody simulation software Recurdyn. It is now possible to anticipate the needle deflection, to get to know about the acting forces and to optimize the geometry of the needle tip.