The electric dipole polarizability and hyperpolarizability of the cis and trans form of formic acid have been calculated at CCSD(T) and DFT levels of theory using Dunning and Sadlej basis sets. The frequency-dependent (hyper)polarizabilities have been obtained for different non-linear optical processes. Dispersion corrections are found to be very modest for (-omega;omega) but sizeable for beta(v)(-omega(sigma);omega(1,) omega(2)) and < y >(-omega(sigma);omega(1), omega(2), omega(3)). DFT, within the B3LYP and PBE1PBE approximations, gives accurate values of dipole moment and dipole polarizability, but seriously overestimates first and second hyperpolarizabilities. It has been found that cis and trans conformations of formic acid could be easily distinguished on the basis of their first hyperpolarizability and depolarization ratio values. (c) 2005 Elsevier B.V. All rights reserved.