The electronic polarization of liquid acetonitrile is investigated using the sequential Monte Carlo/quantum mechanics methodology. Second-order Moller-Plesset and density-functional theory calculations of the dipole moment are performed on statistically uncorrelated structures of liquid acetonitrile generated by the MC simulation. Our best result, obtained at the MP2/aug-cc-pVTZ level, gives an average dipole moment of 4.65 ± 0.19 D, in agreement with an experimental prediction of 4.5 ± 0.1 D. This result corresponds to an increase of 0.71 ± 0.19 D in going from the gas to the liquid state. © 2005 Elsevier B.V. All rights reserved.