The electronic properties of chemically functionalized nanodiamonds are studied using density functional theory calculations. HOMO-LUMO gaps and relative stabilities are calculated for different surface functionalization schemes and diamond nanocrystal morphologies. The effects of chemical decoration on the size and nature of the HOMO-LUMO gap of the various systems considered are discussed in detail. We conclude that surface chemical functionalization has the potential to become an accessible route for controlling the electronic properties of nanodiamonds.