The racemic title compound, trans-[N,N-bis(2-aminoethyl)-1,2-ethanediamine-kappa(4)N](DL-isoleucinato-N,O)cobalt(III) diperchlorate, [Co(C(6)H(18)N(4))(C(6)H(12)NO(2))](ClO(4))(2), crystallizes in the enantiomorphous space group P2(1)2(1)2(1) with Z = 12 (Z' = 3). Each of the three cations in the asymmetric unit represents a different chirality of the isoleucine ligand; two of them are R (or D) and the third is the S (or L) enantiomer. The mixture crystallizes in a so-called unbalanced crystallization, in which the cations adopt a chiral array of composition RRS or SSR, depending on the crystal selected for data collection.