The molecular parameters of cyanofulminate, NCCNO, have been determined in large-scale ab initio calculations using the coupled-cluster method, CCSD(T), and basis sets of double-through quadruple-zeta quality. The equilibrium structure of the molecule was found to be linear, with a strongly anharmonic potential energy function of the CCN bending motion (nu (7) mode). The rotation-bending, energy levels were then calculated using a semirigid-bender Hamiltonian. The vibrational energy levels and effective rotational constants determined for various nu (7) states were found to be in good agreement with the experimental data.