A vibrating-tube densitometer was used for measuring differences in densities between CsBr(aq) and water from molalities of 0.0024 mol.kg-1 to 0.50 mol.kg-1, at temperatures between 604.4 K and 725.5 K, and at pressures from 18.4 MPa to 38.0 MPa. The temperature and molality dependences of the derived apparent molar volumes are compared with those for the other 1-1 electrolytes. Anomalous behavior was observed for dilute solutions in the region of low density of water (rho0 < 350 kg.m-3) where the salts with the lowest ionic radii had the least negative values of the apparent molar volumes. This behavior indicates that the ion pairs with the smallest distance of closest approach have the least negative apparent molar volumes. Using the Pitzer parametric equation and a simplified model describing ion-pairing in dilute solution, the partial molar volumes at infinite dilution were estimated when the density of water was greater than 280 kg.m-3. Under these conditions, there was no evidence that critical-point phenomena invalidated the estimate.