A 3D deformable model is introduced which evolves in true 3D images, under the action of internal forces (describing some elasticity properties of the surface), and external forces attracting the surface toward some detected edges. The formalism leads to the minimization of an energy which is expressed as a functional. The authors use a variational approach and a finite-element method to express the surface in a discrete basis of continuous functions. This leads to a reduced computational complexity and a better numerical stability. The power of the approach to segment 3D images is demonstrated by a set of experimental results on various complex medical 3D images.<>