Ce(Rh0.69Ir0.31)Ge has been investigated by magnetization measurements, differential scanning calorimetry, and X-ray diffraction on a single crystal at 300, 150, and 100 K. For the first time, a decrease of the valence of cerium with decreasing temperature has been observed. This first-order valence transition evidenced at 236-258 K by magnetization measurements is correlated to the occurrence of a structural transition appearing between 300 and 150 K. The structural properties versus temperature of Ce(Rh0.69Ir0.31)Ge are discussed in relation to those determined on single crystals on the antiferromagnet CeRhGe and on the intermediate valence compound CeIrGe. The structure refinements revealed significantly different distortions for the [RhGe] and [IrGe] polyanionic networks, which are a direct consequence of the different electron densities at the rhodium and iridium sites, respectively. The crystal chemical peculiarities of the CeRhGe, Ce(Rh0.69Ir0.31)Ge, and CeIrGe structures are discussed.