At room temperature and atmospheric pressure, the magnitude of the hydration entropy of neutral solutes increases with the molecular volume according to a trend that is largely insensitive to the polar nature of the solute molecule. This general trend is well reproduced by the entropy change upon cavity creation in water as calculated by means of classic scaled particle theory. In contrast, the magnitude of the hydration entropy of the 20 alkali halides decreases on increasing the size of the constituent ions, demonstrating that the strength of charge-water dipole interactions plays the dominant role. (C) 2009 Elsevier B.V. All rights reserved.