The crystal structure of the title compound, deca-methyl-cobaltocene, [Co(C(10)H(15))(2)], has been determined. High-quality single crystals were grown from a cold saturated hexa-methyl-disiloxane solution. The structure is related to the manganese and iron analogs. The molecule has D(5d) symmetry, with the Co atom in a crystallographic 2/m position. The cobalt-centroid(C(5)) distance is 1.71Å and the centroid(C(5))-Co-centroid(C(5)) angle is 180°, by symmetry.