A simple model is presented which explains the origin and magnitude of large permanent electric dipole moments recently observed for CdSe nanorods. It is based on the small crystallographic deviations of the CdSe lattice from the ideal wurtzite structure. The permanent electric dipole moment is found to scale with the volume of the nanocrystal, as observed experimentally. (C) 2003 Elsevier B.V. All rights reserved.