Despite our deep understanding of neuroblastic tumors, some patients still suffer treatment failure, so pre-treatment risk stratification still requires improvement and the search for new therapeutic targets must continue. Here we correlated prognostic clinical and biological features of neuroblastic tumors with the density of extracellular matrix glycosaminoglycans (the main components of the extracellular matrix 'ground substance'), in nearly 400 primary samples. We also studied the relationship between the density of extracellular matrix glycosaminoglycans and the expression of B3GALT6, an enzyme required for their synthesis. We associated a decrease in glycosaminoglycans with neuroblastomas that were histopathologically poorly-differentiated or undifferentiated, as well as with metastatic disease, and 1p36 deleted tumors. This decrease in glycosaminoglycans was also related to abnormal nuclear B3GALT6 expression in neuroblastic cells. These findings point towards the importance of the ground substance in the aggressiveness of neuroblastic tumors, which should therefore be considered when developing novel therapies for treating neuroblastomas.