The molecular complex in a 1:1 ratio of nitrosyl chloride ClNO with hydrogen chloride has been characterized in argon matrices by infrared spectroscopy. Ab initio calculations using the self-consistent-field Hartree-Fock, the second order Moller-Plesset, and the Becke-Lee-Yang-Paar density functional (DFT methods) were undertaken on all possible structures. Only one stable structure was found. It showed simultaneously interaction of the Cl, N, and O atoms of ClNO with the H atom of HCl. The complexation induces a mean variation of about -0.005 Angstrom of the NO bond and about +0.005 Angstrom of the ClN bond. The HCl bond length is calculated to lengthen by about +0.008 Angstrom.