The Raman and infrared bands of trans-stilbene in the ground electronic state (So) and an excited singlet state (S-1) are assigned on the basis of density functional calculations at the 6-311+G** level for the S-0 state and configuration interaction single calculations with the 6-311+G** basis set for the S 1 state. Not only the wavenumbers of normal modes but also Raman activities, Raman depolarization ratios, and infrared intensities are calculated and used for band assignments. The vibrational patterns of some characteristic modes are discussed. It is found that, with respect to a few low-wavenumber modes in both the S-0 and S-1 states, the results of the present calculations are inconsistent with those derived from an analysis of the fluorescence excitation spectra and dispersed fluorescence spectra of trans-stilbene in a supersonic jet.