Dendrimer-star polymers are prepared by grafting monofunctional poly(ethylene glycol) (PEG) chains of low polydispersity onto the terminal groups of poly(amidoamine) (PAMAM) dendrimers. A novel gel permeation chromatography technique is used to calculate the average number of PEG branches ("arms") per star. The maximum number of PEG arms (of M-n = 5000 g mol(-1)) ranges from about 30 arms for a generation 3 dendrimer-star to about 750 arms for a generation 10 dendrimer-star. Radii of gyration of the stars are measured in dilute solution in a good solvent (methanol-d(4)) by small-angle neutron scattering (SANS). The stars have measured radii of gyration of about 6-14 nm. Theoretical dimensions of the stars in dilute solution in a good solvent are calculated by treating the stars as a shell of linear chains tethered to a spherical core. The radii of gyration computed from the core-shell model are consistent with the dilute solution values from SANS.