Syndecans are a four member family of cell surface proteoglycans, which via their heparan sulfate chains can bind both extracellular matrix molecules and heparin-binding growth factors. In signal transduction they cooperate with tyrosine kinase receptors and thus can participate in the regulation of cell growth and behaviour. Besides the fact that their developmental expression follows morphogenetic rather than histological boundaries, also changes in their expression take place during development of diseases. Among these, the loss of syndecan expression during malignant transformation suggests that syndecans could play a role in restricting tumor growth and metastasis.