Level-sets provide powerful methods for the segmentation of deformable structures. They are able to handle protrusions and specific topological effects. In this work a particle system formulation of level-sets is introduced. It keeps all the advantages of the levelset approach for the segmentation of deformable structures, while it overcomes some of its drawbacks. In this approach the level-sets are controlled by particles, which is of particular interest for interactive control. The particle system records the internal energy of the level-set, while the external force field comes from image data. The energy minimization process is fast, stable and robust. The use of skeleton techniques provide a reliable intialization of the particles, and it is coherent with simple affine motion. The paper is illustrated by examples coming from real image sequences.