The adsorption of polydisperse, interacting nanoparticles is studied experimentally and discussed in terms of the random sequential adsorption model. Two kinds of polystyrene particles with different size variation (41 +/- 6 and 107 +/- 5 nm) were used in adsorption experiments at or close to saturation. The dried monolayer particle films were analyzed with scanning electron microscopy. Selective adsorption of smaller particles resulted in altered size distributions on the surface compared to that in solution. Varying the ionic strength was seen to influence the effective polydispersity of the particles. With increasing salt concentration there was a relative increase in the adsorption of smaller particles, resulting in a large shift toward smaller particle sizes in the size distribution on the surface. Polydispersity gave a slight increase in coverage at high salt concentrations and a decrease in the ordering of the particles on the surface.