In this paper, we describe a new method for surgery simulation including a volumetric model built from medical images and an elastic modeling of the deformations. The physical model is based on elasticity theory which suitably links the shape of deformable bodies and the forces associated with the deformation. A real-time computation of the deformation is possible thanks to a pre-processing of elementary deformations derived from a finite element method. This method hasbeen implemented in a system including a force feedback device and a collision detection algorithm. The simulator works in real-time with a high resolution liver model.