Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-inflammatory activity in vivo and thus represents a promising candidate for therapeutic and diagnostic applications. To investigate the in vivo pharmacokinetics in detail, dPGS with a molecular weight of approx. 10 kDa was radiolabeled with 3H and 64Cu, and evaluated by performing biodistribution studies and small animal positron emission tomography (PET). 3H-labeling was accomplished by an oxidation–reduction process with sodium periodate and [3H]-borohydride. 64Cu-labeling was achieved by conjugation of isothiocyanate- or maleimide-functionalized copper(II)-chelating ligands based on 1,4-bis(2-pyridinylmethyl)-1,4,7-triazacyclononane (DMPTACN) to an amino functionalized dPGS scaffold, followed by reaction with an aqueous solution containing 64CuCl2. Independent biodistribution by radioimaging and PET imaging studies with healthy mice and rats showed that the neutral dPG was quantitatively renally eliminated, whereas the polysulfated analogues accumulated mainly in the liver and spleen. Small amounts of the dPGS derivatives were slowly excreted via the kidneys. The degree of uptake by the reticuloendothelial system (RES) was similar for dPGS with 40% or 85% sulfation, and surface modification of the scaffold with the DMPTACN chelator did not appear to significantly affect the biodistribution profile. On the basis of our data, the applicability of bioactive dPGS as a therapeutic agent might be limited due to organ accumulation even after 3 weeks. The inert characteristics and clearance of the neutral polymer, however, emphasizes the potential of dPG as a multifunctional scaffold for various nanomedical applications.