Using first principles, total energy method based on the full potential linear augmented plane wave method, we have performed theoretical studies of the relative stabilities of the substoichiometric CuI. A study of the electronic structure was undertaken, which revealed vacancy induced peaks in the DOS. The electron densities attached to these peaks have been analysed and are found to emanate from the unscreened Cu-Cu bonds through the iodine vacancy site. (C) 2003 Published by Elsevier B.V.