Diffraction data recorded at low temperature with Mo K\alpha from two different crystals have been used in the refinement of the structure of the acid rhodo complex salt, \mu-hydroxo-bis[pentaamminechromium(III)] chloride monohydrate [(NH3)5CrOHCr(NH3)5]Cl5.H2O. Several structural models in two different tetragonal space groups have been investigated before a satisfactory description of the structure was obtained. The compound crystallizes in the orthorhombic space group P212121, with a= 16.155 (3), b = 16.154 (3), c = 14.750 (7) Å and Z = 8. The apparent tetragonal symmetry arises due to rotation twinning of the crystals. The diffraction pattern is further complicated by tetragonal pseudo-symmetry of the chromium sites, which means that reflections with l = 2n + 1 are systematically weak. The two independent dimeric cations are involved in slightly different hydrogen-bond patterns. This observation and the relative orientation of the dimers in the crystal is in accordance with spectral and magnetic measurements.