Single particle dark field spectroscopy has been combined with high-resolution scanning electron and atomic force microscopy to study the scattering spectra of single gold/silica nanoshells. The plasmon resonant peak energies match those calculated by Mie theory based on the nanoshell geometry. The resonance line widths fit Mie theory without the inclusion of a size-dependent surface scattering term, which is often included to fit ensemble measurements. These results suggest that plasmon spectral measurements of nanoparticle ensembles are broadened due to particle inhomogeneity.