In the literature, there is a striking controversy concerning the basic physical properties of UIr2Zn20 crystals that have been recently measured by various research groups. One may suppose that the particular samples are not free of defects and this is the likely reason for the discrepancy between the reported key experimental results. Here, positron annihilation spectroscopy serves as a very sensitive tool to probe lattice perfection with respect to the presence of open-volume defects. In the present work, we perform calculations of the electron density of states (DOS), positron distribution, and positron lifetime, τ, in the UIr2Zn20 perfect crystal of Fd-3m cubic structure (according to our best knowledge, for the first time in the literature). The results are compared with their counterparts for the crystals containing an Ir and Zn1 monovacancy. Three sharp narrow peaks from 5f U electrons are observed in the DOS close to the Fermi energy, EF, both for the perfect crystal as well as for the one containing vacancies. These peaks are located below, above and just at the Fermi level. Two peaks originate from f5/2 and f7/2 states, while the existence of the remaining one may be interpreted in terms of the dual character of uranium f electrons. The presence of vacancies considerably redistributes the positron charge in the unit cell and, in consequence, increases the value of the positron lifetime as compared with the perfect material.