We performed molecular dynamics (MD) simulations of one or two copies of polyethylene glycol of molecular weight 550 (PEG550) and 5000 (PEG5000) daltons, conjugated to generation 3 (G3) to 5 (G5) polyamidoamine (PAMAM) dendrimers with explicit water using a coarse-grained model. We found the radii of gyration of these dendrimer-PEG molecules to be close to those measured in experiments by Hedden and Bauer (Hedden, R. C.; Bauer, B. J. Macromolecules 2003, 36, 1829.), Densely grafted PEG ligands (>50% of the dendrimer Surface) extend like brushes, with layer thickness in agreement with theory for starlike polymers. Two dendrimer-PEG complexes in the box drift away from each other, indicating that no aggregation is induced by either short or long PEG chains. conflicting with a recent view that the cytotoxicity of some PEGylated particles might be due to particle aggregation for long PEG lengths.