The preparation of pure, stable aminoacetonitrile (1-amino-, 1′-cyanomethane) CH2NH2CN (1) is described. The Raman spectrum, now complete, and a novel infrared spectrum extending over the 50–3600 cm−1 region are reported. A tentative normal vibration analysis is presented and supported by Raman and infrared data from the spectra of CH2NHDCN (2) and CH2ND2CN (3), the interpretation being compatible with Cs symmetry (1 and 3) in accordance with McDonald and Tyler's results from microwave studies of 1, 2, and 3. The predominance of the trans rotamer may be attributed to intramolecular hydrogen bonding but this is too unimportant to influence the vibrational frequencies of gaseous 1, 2, and 3. However, large gas/liquid frequency shifts occur, quite possibly due to intermolecular hydrogen bonding in the liquid phase.