Isomerization and dissociation of the vinylamine radical cation [CH2=CHNH2].+ (1.+) was explored by using both mass spectrometric techniques and molecular orbital calculations. The ground-state potential energy surface of [C2H5N].+cations containing the CCN frame was examined by ab initio molecular orbital calculations terminated at the PUMP4/6-311++G**//MP2/6-31G**+ZPE level. The global minimum corresponds to the vinylamine radical cation [CH2=CHNH2].+ (1.+), which is 81 and 122 kJ/mol more stable than [CH3CNH2].+ (2.+) and [CH3CHNH].+ (3.+) ions, respectively. Isomerization and dissociation of 1.+ into [C2H4N]+ + H. were evaluated in detail. It is demonstrated that the methylaminocarbene ion 2.+ is an important reaction intermediate, and in particular, the lowest energy process from 1.+ is isomerization into 2.+ followed by elimination of a hydrogen atom to generate N-protonated methyl cyanide. Formation of the latter is confirmed by tandem mass spectrometry experiments and proton transfer between [1 - H]+ ions and several reference bases conducted in a Fourier transform mass spectrometer.