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The electronic structure of the endohedral complex U@$C28$ was studied using ab initio quantum chemical methods including relativistic core potentials, gaussian double zeta basis sets, and spinorbit configuration interaction calculations. The self consistent field population analysis shows extensive mixing of U 6d and 5f orbitals with $C\pi$ orbitals, indicating strong binding. The ground state is found to have two singly occupied orbitals. one principally $C\pi \ast$ in character (e symmetry) and one principally U 5f in character (a1 symmetry). The combined space-spin (double group) symmetry is E and is principally of singlet character. This state is diamagnetic, but there are two very low-lying paramagnetic excited states. Groups of excited states are found at roughly 0.1 eV intervals.