Gold nanoparticles are readily oxidized by Au(III) in the presence of cetyl-trimethylammonium bromide (CTAB). Oxidation occurs preferentially at surface sites with higher curvature. Conversely, oxidation with cyanide ions in the absence of CTAB leads to uniform oxidation over the whole surface. Examples of the spatially directed oxidation are provided using large, irregular spheres, nanocubes, and nanorods. We conclude that the mechanism of oxidation depends on whether the oxidant is attached to CTAB micelles. It is postulated that the CTAB micelles approach the narroparticles preferentially at the tips, leading to spatially directed oxidation.