The massspectra of the dichloro- and bromochloro-cyclobutanes, the dichlorocyclopentanes, and the dichloro-, chlorofluoro-, and stable dibromo-cyclohexanes are reported. Four major breakdown pathways can be distinguished, the favoured fragmentation route depending on the ring size, the type of halogen substitution, the the relative position, and cis–trans-relationships of the two substituents. Within