The molecular structure and the stability of neutral, anionic, and dianionic tetracyanoethylene (TCNE) have been studied with MP2, coupled-cluster (CC), and density functional theory (DFT) procedures. The optimized geometries are in agreement with the available experimental data, although significant deviations for the CdropN bond distance have been obtained at the MP2 level. The adiabatic electron affinity of TCNE calculated with the B3LYP method is overestimated by 0.32 eV. In the light of the CC results, the source of such an overestimation is suggested to lie on the theoretical approach, rather than on a too low experimental value. (C) 2003 Elsevier Science B.V. All rights reserved.