We have calculated self-consistent field (SCF) and second-order Moller-Plesset perturbation theory (MP2) for the dihaloethynes X-Cequivalent toC-X, X = F, Cl, Br and I. All calculations have been performed with carefully optimized, flexible basis sets of gaussian-type functions. Our best values for the quadrupole moment (Theta/ea(0)(2)) are -0.6524 (FCCF), 3.6612 (ClCCCl), 5.8143 (BrCCBr) and 8.3774 (ICCI). The dipole polarizability is strongly anisotropic. For the mean ((α) over bar /e(2)a(0)(2)E(h)(-1)) and the anisotropy (Deltaalpha/e(2)a(0)(2)E(h)(-1)) we obtain 23.58 and 15.09 (FCCF), 51.75 and 48.30 (ClCCCl), 66.53 and 60.04 (BrCCBr), 93.79 and 78.91 (ICCI). The mean dipole hyperpolarizability ((γ) over bar/(e)4a(0)(4)E(h)(-3)) increases rapidly as 2932 (FCCF), 9924 (ClCCCl), 17409 (BrCCBr) and 35193 (ICCI). The transversal component of the hyperpolarizability is larger than the longitudinal one for FCCF, gamma(xxxx) > gamma(zzzz) but this is reversed for the other molecules in the series. Difluoroethyne is less (hyper)polarizable than ethyne.