It is shown that electrons associated with vortices may be self-trapped by lattice deformations. In essence, the deformation creates a well in which part of the electrons associated with vortex cores are trapped. The effect is strongest in superconductors which have a strong electron-phonon coupling, a large coherence length and a significant ratio Δ/ε_F. The associated lattice deformations have been observed in a spin-polarised neutron scattering experiment on superconducting Nb.