Coating the surfaces of inorganic nanoparticles with polyethylene glycol (PEG) is an important step in the development of many nanoparticle-based drug delivery systems. The efficiency with which drug molecules can be loaded on to nanoparticle surfaces is contingent on the concentration, distribution and stability of the PEG coating. In this study the distribution and relative stability of PEG on diamond nanoparticles is predicted, for clean and passivated surface structures, in 3D. This is an ideal exemplar, since PEGylated diamond nanoparticles are already being trialed as carriers for doxorubicin (DOX). The results show that PEGylation is favorable near the {100} facets regardless of surface reconstructions or pre-treatment, but pre-treatment is required to increase the probability of stable and homogeneous PEGylation on other facets.