We present here the first comprehensive structural characterization of peptide dendrimers using molecular simulation methods. Multiple long molecular dynamics simulations are used to extensively sample the conformational preferences of five third-generation peptide dendrimers, including some known to bind aquacobalamine. We start by analyzing the compactness of the conformations thus sampled using their radius of gyration profiles. A more detailed analysis is then performed using dissimilarity measures, principal coordinate analysis, and free energy landscapes, with the aim of identifying groups of similar conformations. The results point to a high conformational flexibility of these molecules, with no clear "folded state", although two markedly distinct behaviors were found: one of the dendrimers displayed mostly compact conformations clustered into distinct basins (rough landscape), while the remaining dendrimers displayed mainly noncompact conformations with no significant clustering (downhill landscape). This study brings new insight into the conformational behavior of peptide dendrimers and may provide better routes for their functional design. In particular, we propose a yet unsynthesized peptide dendrimer that might exhibit enhanced ability to coordinate aquocobalamin.