1,1-Dilithioethylene　is　a　prototypical　carbon-lithium　compound　that　is　not　known　experimentally.　All　low-lying　singlet　and　triplet　structures　of　interest　were　investigated　by　using　high-level　theoretical　methods　with　correlation-consistent　basis　sets　up　to　pentuple　zeta.　The　coupled　cluster　methods　adopted　included　up　to　full　triple　excitations　and　perturbative　quadruples.　In　contrast　to　earlier　studies　that　predicted　the　twisted　C-2v　triplet　to　be　the　ground　state,　we　found　a　peculiar　planar　C-s　singlet　ground　state　in　the　present　research.　The　lowest　excited　electronic　state　of　1,1-dilithioethylene,　the　twisted　C-s　triplet,　was　found　to　lie　9.0　kcal　mol(-1)　above　the　ground　state　by　using　energy　extrapolation　to　the　complete　basis　set　limit.　For　the　planar　C-s　singlet　and　twisted　Cs　triplet　states　of　1,1-dilithioethylene,　anharmonic　vibrational　frequencies　were　reported　on　the　basis　of　second-order　vibrational　perturbation　theory.　The　remarkably　low　(2050　cm(-1))　C-H　stretching　fundamental　(the　C-H　bond　near　the　bridging　lithium)　of　the　singlet　state　was　found　to　have　very　strong　infrared　intensity.　These　highly　reliable　theoretical　findings　may　assist　in　the　long-sought　experimental　identification　of　1,1-dilithioethylene.　Using　natural　bond　orbital　analysis,　we　found　that　lithium　bridging　structures　were　strongly　influenced　by　electrostatic　effects.　All　carbon-carbon　linkages　corresponded　to　conventional　double　bonds.