The following bond lengths (r g ) and bond angles have been determined for perfluoroadamantane from gas-phase electron diffraction: C-C 1.560 +/- 0.003, C(F 2 )-F 1.340 +/- 0.005, C(F)-F 1.363 +/- 0.010 Å, CC(F 2 )C 107.7 +/- 0.9, CC(F)C 110.3 +/- 0.4, FC(F 2 )F 106.9 +/- 0.4, C(F 2 )CF 108.6 +/- 0.4 and C(F)CF 110.5 +/- 0.2 o . Perfluorination is found to expand the adamantane cage, characterized by a 0.02 Å lengthening of the C-C bonds.