Abstract The structure and conformational stability of isocyanatoacetaldehyde were investigated using ab initio calculations. The calculations were carried out at RHF/6-311G* and MP2/6-311G* levels. From the calculation the molecule was predicted to exist predominantly in the cis–cis conformation. The potential function for the internal rotation of the CHO group was determined for the molecule. The inclusion of electron correlation into the calculations had a very small effect on the calculated potential coefficients. The vibrational frequencies were computed at the Hartree–Fock level. Normal coordinate calculations were carried out and potential energy distributions were calculated for the cis–cis conformer of the molecule. The calculated vibrational frequencies for the two conformers were scaled and compared to those observed experimentally for similar molecules.