Hydrous Ir oxide films have been studied using cyclic voltammetry, ac impedance, and ellipsometric techniques. Under certain conditions of exposure after oxide growth, an irreversible decrease of the Ir(+III)/Ir(+IV) conversion kinetics, also referred to as irreversible film aging, is observed. However, these films are thermodynamically not unaltered and the film charge is not lost during aging. Aging of Ir oxide films involves the detachment of oxide segments from the Ir substrate and/or cracking within the oxide itself. This leads to an increase in the characteristic transport length and a possible explanation of the altered kinetics. Furthermore, Ir oxide film aging can be prevented, depending on the conditions employed to grow and subsequently study them.