The hydrolysis of aluminum salts in aqueous solution has been studied by Raman spectroscopy. Evidence for the occurrence of the ion [Al13O4(OH)24(OH2)12]7+ in solutions containing a formal [OH–] : [Al3+] ratio of 2.5 : 1 is provided by comparisons with the spectra of crystalline compounds containing this ion. The presence of other polymeric species in less highly hydrolysed solutions cannot be confirmed.