By use of crystals from the Werner collection at the University of Zurich, the X-ray structure of a (mu -amido)(mu -hydroxo)(mu -superoxo)dicobalt(III) salt, probably synthesized around 1909, was determined. This complex is apparently the first dimetallic species with three bridging ligands of such a composition. The O-O bond distance of 1.340(4) Angstrom is consistent with. coordinated superoxo anion, and the two cobalt atoms are 2.776(1) Angstrom apart.