Intracellular or extracellular deposition of highly ordered fibrillar aggregates is a characteristic of protein misfolding diseases. Proteins can aggregate alone in vitro; however, deposits of fibrillar aggregates in vivo contain a number of proteinaceous and non-protein components in addition to the major protein that forms the aggregates. These components are thought to play critical roles in the pathology of protein misfolding diseases. Among these components, glycosaminoglycans (GAGs), which are heteropolysaccharides that occur in all mammalian tissues, are modified by sulfation that determines specific interactions between GAGs and their protein ligands. This mini-review summarizes our current understanding of how sulfated GAGs contribute to the pathology of protein misfolding diseases, with a particular focus on amyloidosis.