The reaction between Co(NH3)5OH23+ and CrO42- at pH 6.5 in aqueous solution produces [Co(NH3)5CrO4](ClO4), which has been characterized by a single crystal X-ray diffraction study. Brown crystals of the complex are orthorhombic, with space group Cmc21 and lattice constants a=10.120(3), b=12.431(3), c=8.591(1) Å and Z=4. The structure consists of discrete Co(NH3)5CrO4+ and ClO4- ions, each of which is centred on a mirror plane such that asymmetric repeat unit is comprised of half the formula unit. The cation may be considered as a cobalt(III) octahedral environment linked to a tetrahedrally coordinated chromium (VI) centre through a common oxygen atom. Deviations from idealized Co(III) octahedral geometry arise from steric effects and significant intra- and intermolecular hydrogen bonding.