Polarizability of the sulfate dianion solvated in water clusters and in an extended water slab is investigated by a combination of ab initio calculations and classical and Car-Parrinello molecular dynamics. Quantum chemistry calculations at the MP2/aug-cc-pvdz level are performed for structures obtained from molecular dynamics simulations replacing water oxygens and hydrogens by fractional point charges. Sulfate polarizability in bulk water amounts to roughly 7 Angstrom(3). Despite this large value SO42- clearly prefers interior over surface solvation, in accord with previous experimental evidence for large aqueous clusters. (C) 2002 Elsevier Science B.V. All rights reserved.