The harmonic frequencies of acetaldehyde, acetaldehyde-d(1), and acetaldehyde-d(4) were obtained experimentally via a comprehensive analysis of the molecules’ infrared vibrational spectra. Specifically, the observed fundamental frequencies were corrected for anharmonicity by applying an extensive list of anharmonic factors derived from the overtone and combination bands assigned to features in the infrared spectra of CH3CHO, CH3CDO, and CD3CDO. An ab initio harmonic force field calculated at the MP2/6-311++G(3df,p) level of theory yielded fundamental frequencies that were an average of 1.6% too large relative to the experimentally obtained harmonic values. The theoretical force constants were subsequently refined through a least squares fit to the experimental harmonic frequencies. The results of the normal coordinate analysis were then used to convert the acetaldehyde-d(0), -d(1), and -d(4) isotopomers’ measured absolute intensities to atomic polar tensors. The final potential function was successfully used to predict the observed vibrational spectrum of acetaldehyde-d(3) and led to the reassignment of the v(5), v(12), and v(13) vibrational bands in the CD3CHO infrared spectrum.