The synthesis and characterization of the stable carbene perdeuterio-1,3,4,5-tetramethylimidazol-2-ylidene (2) are reported. The neutron and X-ray diffraction data from single crystals of this perdeuterocarbene are used to determine the electron distribution in the molecule. Neutron diffraction data were collected at 80 and 173K on 2. The experimentally determined electron density is very closely matched by density functional calculations which show that 2 is a true carbene with negligible ylidic character.