The equilibrium geometries of hexafluorocyclobutene, 3,3,4,4-tetrafluorocyclobutene, and cyclobutene are determined employing quantum chemical calculations at the MP2/6-31+G* and LDA+BP/TZP levels of theory and compared to the structural parameters determined experimentally by microwave spectroscopy and electron diffraction techniques. The theoretical results are in better overall agreement with the latter set of experimental data and substantiate the experimental finding of a remarkably long C(3)-C(4) bond in hexafluorocyclobutene. The origins of the structural changes upon fluorination are discussed on the basis of qualitative concepts such as rehybridization, Coulombic interaction, hyperconjugation, and pi-back-bonding.