An interaction potential between the hydrated ion, [Cr(H2O)(6)](3+), and a water molecule has been developed starting from restricted open-shell Hartree-Fock (ROHF) ab initio calculations using DZV basis sets. The importance of many-body effects associated with this potential is examined up to the level of a cluster including the second hydration shell. Monte Carlo simulations of Cr3+ aqueous solutions using this potential for hydrated ion-solvent interactions and the MCY for water-water interactions have been performed. The influence of the number of water molecules employed for simulations has been examined by performing simulations with 210 and 512 water molecules. Structural results derived from simulations indicate a well-defined second hydration shell. The Cr-O and Cr-H radial distribution functions (RDFs) show maxima around 4.06 and 4.49 Angstrom, giving integration numbers of similar to 14 and 36, respectively. Evidence of a diffuse third hydration shell is also shown by the Cr-O RDF. The Cr3+ hydration energy is slightly overestimated with respect to the experimental value. Advantages and limitations of the hydrated ion approach in computer simulations are discussed.