AbstractEighteen quite different examples are discussed in which the unimolecular elimination of a given radical X˙ from an odd‐electron cation cannot be described as a one‐step process. Despite the fact that the radical X˙ eliminated is already present as a structural unit in the decomposing ions, the product analysis and structure determination of the even‐electron ion formed, the investigation of the energetics of the reaction, the analysis of stereochemical factors, and the determination of kinetic isotope effects reveal that the eliminations must be characterized as two‐ or multi‐step reactions. In all cases investigated, the process commences with a specific (intramolecular) hydrogen transfer to a suitable acceptor function. In this way a reactive radical site is created which induces the actual dissociation step (elimination of X˙) by simultaneous double bond formation. Due to the fact that the hydrogen migration takes place within the charge carrying part of the cation radical and that the migrated hydrogen atom remains there throughout the whole process, the intervention of a H‐migration cannot be traced directly by appropriate mass shifts in the spectra of 2H labelled precursors. However, the methods mentioned above can be applied to reveal the details of the reaction mechanism, and the term ‘hidden’ hydrogen migration induced dissociation is suggested to recognize the particular rǒle of H‐rearrangements to trigger radical eliminations from odd‐electron cations in the gas phase.