The cell-to-cell variation of gold nanoparticle (GNP) uptake is important for therapeutic applications. We directly counted the GNPs in hundreds of individual cells, and showed that the large variation from cell-to-cell could be directly modelled by assuming log-normal distributions of both cell mass and GNP rate of uptake. This was true for GNPs non-specifically bound to fetal bovine serum or conjugated to a cell penetrating peptide. Within a population of cells, GNP content varied naturally by a factor greater than 10 between individual cells.