The vibronic pattern of the resonance Raman spectrum of cyclobutene is simulated by ab initio molecular orbital and by density functional theory calculations. Both Franck-Condon and Herzberg-Teller contributions are included in the analysis of the spectrum. The results suggest an initial dynamics of cyclobutene in the S-1 excited state in which the molecule attempts a cis-trans isomerization of the ethylene moiety.