Dengue virus (DENV) and hepatitis C virus (HCV), members of the family Flaviviridae, are global human health concerns. As positive-strand RNA viruses, they each replicate in the cytoplasm of infected cells and induce distinct membranous replication compartments where most, if not all, steps of the viral life cycle occur. This Gem briefly reviews the most recent insights into the architecture and functional properties of membranous replication and assembly sites induced by DENV and HCV.