The vibronic mechanisms responsible for the appearance of several false origins in the two-photon spectrum of naphthalene have been investigated theoretically. The relevant vibronic terms have been computed in the “floating orbital” scheme by using CNDO/S wavefunctions, while the normal coordinates have been obtained by using a MINDO/3 program. The calculated relative intensities of the b2u modes result in satisfactory agreement with the experimental findings. The main contribution to the most intense mode, ν21, is found to derive from a strong coupling between the lowest excited B2u state and the ground state. The feature explains the anomalous increase of the frequency of this mode in the S1(B2u) state with respect to the ground state.