The vibrational sum rule has been applied to the fluoro-chloro-bromo-ethylenes and good agreement obtained between observed frequency sums and those calculated on the basis of additivity considerations. Two unobserved frequencies for trans dibromoethylene have been calculated and the in-plane and out-of-plane sums for some molecules not yet investigated. Several ambiguities with regard to some halogenated ethylenes have been resolved and several assignments which merit reinvestigation have been indicated.