Abstract This paper, reports the infrared spectrum of cyclohexane (100–3400 cm−1) and of cyclohexane-d12 (300–3400 cm−1), and the Raman spectrum with polarizations for both compounds. With these data the vibrational assignments have been advanced considerably. Suggestions have been made for all but two of the spectroscopically-active fundamentals, but four totally-inactive frequencies are still unknown. The data for the deuterated molecule have required extensive modifications in the previous assignments. One puzzling feature is the rather strong evidence for a methylene rocking frequency at 384 cm−1 in cyclohexane, which is startlingly low.