The Raman and infrared spectra of crystalline methyl 3,6-dideoxy-β-D-ribo-hexopyranoside monohydrate in the O—H stretching region have been studied at room temperature and lower temperatures. Four bands have been identified and correlated with the corresponding O … O distances of the four distinct hydrogen bonds obtained from X-ray data. The assignments were substantiated by a deuterium isotopic dilution study.