Ab initio calculations are carried out for FH–PH3 and ClH–PH3 using a basis set including two sets of polarization functions. Electron correlation is incorporated via Møller–Plesset perturbation theory to second and (in part) to third orders. The basis set is tested and found to produce satisfactory treatments of subsystem properties including geometries and dipole moments as well as the proton affinity and inversion barrier of PH3. Electron correlation is observed to markedly enhance the interaction between PH3 and the hydrogen halides. Its contribution to the complexation energy is 30% for FH–PH3 and 50% for ClH–PH3. Moreover, the equilibrium geometries of the complexes at correlated levels are quite different than SCF structures.