The structures and energetics of the C2H2N and C2H2N+ isomers have been investigated using a modified Gaussian-2 (G2) method, which takes into account the energy correction due to spin contamination. At the QCISD(Full)/6-31G(d) level, C2H2N may exist as 12 stable isomers. In the order of decreasing stabilities, they are CH2CN (1), CH2NC (2), CHCNH (3), c-CH2CN (4), c-NCHCH (5), CHNCH (6), NH2CC (7), NHCHC (9), c-NHCHC (10), cis-CHCHN (12), cis-CHNHC (13), and trans-CHNHC (14). On the other hand, there are seven C2H2N+ isomers. In the order of decreasing stabilities, they are c-NCHCH+ (5(+)), CH2CN+ (1(+)), CH2NC+ (2(+)), CHCNH+ (3(+)), CHNCH+ (6(+)), c-NHCHC+ (10(+)), and NH2CC+ (7(+)). The G2, result for the ionization energy of 1 and the Delta H degrees(f298) values of 1 and 1(+) are in good agreement with the available experimental data. However, the G2 results for radicals 2 and 5 as well as cations 2(+) and 5(+) do not agree with the experimental data in the literature. This calls for a reexamination of the experimental results. Furthermore, in a recent study of the reaction between nitrogen atom and vinyl radical, a C2H2N radical was formed with an ionization energy < 9.64 eV. On the basis of our calculations and known reactivity of the reactants, it is concluded that the unidentified isomer is likely to be 2.