The translationally controlled tumour protein (TCTP) is a highly conserved protein that is widely expressed in all eukaryotic organisms. Based on its sequence, TCTP was listed as a separate protein family in protein databases but the recent elucidation of the solution structure of the fission yeast orthologue places it close to a family of small chaperone proteins. The molecular functions determined so far, Ca(2+)- and microtubule-binding, have been mapped to an alpha-helical region of the molecule. TCTP expression is highly regulated both at the transcriptional and translational level and by a wide range of extracellular signals. TCTP has been implicated in important cellular processes, such as cell growth, cell cycle progression, malignant transformation and in the protection of cells against various stress conditions and apoptosis. In addition, an extracellular, cytokine-like function has been established for TCTP, and the protein has been implicated in various medically relevant processes.