The spin distribution in a stable nitroxide biradical that shows ferromagnetic interactions in the solid phase has been studied at three levels of theory: First, at the UHF level; then, including correlation effects in UMP2 calculations; and finally, the results are compared with the spin density obtained using the local density functional (LDF) approximation. It is shown that LDF spin densities are closer to UMP2 than to UHF predictions; the difference between the UHF and the (UMP2, LDF) results points to a redistribution of the spin repartition between N and O due to electronic correlation. For planar conformations of the NO group, there is symmetric distribution (D2d) of the spin density on the adamantane skeleton. For nonplanar nitroxides, the molecule is chiral (C2), which results in a breakdown of the spin transmission on part of the adamantane cage.