Ab initio calculations of the static- and frequency-dependent dipole polarizability α and first and second hyperpolarizabilities β and γ of HCl are presented. Static polarizabilities are determined using the self-consistent field (SCF), second-order Møller-Plesset perturbation theory (MP2), the coupled-cluster single and double excitation method (CCSD), and CCSD with a perturbative estimate of triple excitations [CCSD(T)]. The effect of basis set expansion, particularly the addition of diffuse functions up to g type, is explored. It is found that for highly accurate calculations, f functions are necessary on Cl, but g functions have a much smaller effect. The frequency-dependent hyperpolarizabilities for wavelengths of 694.3 and 1319 nm are determined at the SCF and MP2 levels of theory. The CCSD(T) static values, scaled using MP2 dispersion, are found to be in good agreement with experiment. Electron correlation is found to play a significant role in both the static and dynamic quantities. Use of the SCF dispersion as a percentage correction to the static MP2 hyperpolarizability, however, is found to be a good approximation to the total MP2 frequency-dependent hyperpolarizability at the frequencies studied. The effects of vibrational contributions to the polarizabilities are discussed. © 1992 American Institute of Physics.