Extensive nb initio computations have been carried out to characterize the energy of trans-aziridine-2-carbonitrile relative to cis-aziridine-2-carbonitrile (also known as 2-cyanoaziridine). Correlation consistent basis sets of double-, triple-, quadruple-, and pentuple-zeta quality have been employed to approach the one-particle basis set limit for energies obtained with the restricted Hartree-Fock method and second-order Moller-Plesset perturbation theory. Contributions from higher-order excitations have been determined with the popular coupled-cluster technique which includes single and double excitations as well as a perturbative estimate of triple excitations [CCSD(T)] and with the Brueckner doubles method including a perturbative estimate of triple as well as quadruple excitations [BD(TQ)]. From a focal point analysis, the electronic energy separation is found to be 3.62 kJ mol(-1), which is in excellent agreement with previous theoretical estimates, but is in disagreement with an experimentally estimated lower bound to the free energy difference of 11 kJ mol(-1). The electronic energy of the transition structure connecting the two conformers was determined to be 77.15 kJ mol(-1) higher than the cis-isomer.