Ten basis sets of double and triple-zeta quality augmented by polarization and diffusion function in conjunction with density functional theory (DFT, with the Becke-Lee-Yang-Parr exchange-correlation potential), Moller-Plesset MP2 to MP4 (SDTQ), coupled cluster with single and double excitations (CCSD) and CCSD with perturbative triple excitation [CCSD(T)] levels of theory were applied in studies of the molecular geometry and stability of the H2CO ... HCl complex. Interaction energy (corrected for the basis set superposition error and zero-point vibrational energy contributions) predicted at three highest levels used; the MP4(SDTQ)/6-311++G(2df,2pd)/MP2/ 6-311++G(2df,2pd), CCSD(T)/6-311G(2d,2p)//CCSD/6-311G(2d,2p), and MP2/aug-cc-pVTZ (augmented correlation consistent polarized valence triple-zeta)llMP2/6-311+G(2df,2pd) amounts to -2.65, -2.61, and -3.88 kcal/mol, respectively, while the DFT/6-311++G(2df,2pd) level gives -2.86 kcal/mol. It appears that within a given computational method (e.g., MP2, DFT) interaction energy slightly depends on the chosen reference geometry (e.g., optimized at HE MP2, CCSD, or DFT levels). A significant influence of the BSSE on the interaction energy and molecular geometry of the complex is analyzed. Reliable MP2/6-311++G(2df,2pd) and CCSD/6-311G(2d,2p) levels of harmonic frequencies, infrared intensities and potential energy distribution analysis are presented for the complex and its components and compared to the available experimental data.