Results of a dielectric relaxation study of the aqueous solutions of KCl and CsCl at 25 degreesC are reported using measurements with a vector network analyzer (0.2 less than or equal to nu/GHz less than or equal to 20) and with waveguide interferometers (27 less than or equal to nu/GHz less than or equal to 89). Similar to previously reported data for NaCl,, the spectra of both salts are well fitted by a Cole-Cole equation, although a double-Debye model is competitive at intermediate CsCl concentrations. The impact of the solute on the water structure, reflected in a decrease in the bulk-water relaxation time with rising electrolyte concentration, decreases in the sequence NaCl > KCl > CsCl and appears to be proportional to the surface-charge density of the cation. The interactions of K+ and Cs+ with their hydration shells are too weak to cause irrotational bonding of H2O molecules. It is argued that CsCl exhibits weak ion pairing, although the data are not sufficiently accurate to determine the extent of association and the nature of the ion pair formed.