Rutherford backscattering, channeling of fast ions, and characteristic X-ray radiation at ion excitation were used to investigate the atomic composition and structural variation of single crystals YBa2Cu3O6.0-7.0 (with Al impurity and without it) iodized under identical conditions. The iodine interaction with the crystal lattice was found to depend on the initial amount of oxygen. The oxygen-rich crystals (Tc = 92 K) demonstrated no consequences of their interaction with iodine. At the same time the crystals of the orthorhombic (Tc to approximately 55-60 K) and tetragonal phases showed the change of the atomic composition and the formation of the amorphous surface layers of different thickness to the extent that the sample collapsed. No ordered incorporation of iodine into the Y-Ba-Cu-O crystal structure was found.