The mass spectrometric fragmentation of the stereoisomers of all bicyclo[2.2.1]heptanediols with secondary OH-groups and their methyl ethers has been investigated and some reactions have been studied by deuterated compounds. Stereochemical controlled fragmentations, expected by analogy with cycloalkane diols and their methyl ethers 1–3 have not been observed because of fast ring fragmentations. An exception is the elimination of water with participation of both OH groups, which occurs preferably owing to the spatial arrangement of neighbouring groups and leads to an increase in the intensity of the ions (M—H 2O) +·. By means of the mass spectra, positional isomers of bicyclo[2.2.1]heptane diols, and in most cases also stereoisomers, can be distinguished from each other. The mass spectra of the methyl ethers resemble each other closely.