The molecular structure of free bis(trifluoromethyl) peroxydicarbonate, CF3OC(O)O-OC(O)OCF3, was investigated by the concerted use of gas electron diffraction and theoretical calculations of various quantities (geometry, energy, vibrational; frequencies, C-13 NMR chemical shifts). This combined approach justified the assumption that the syn-syn-syn-syn structure with C-2 overall symmetry (both CF3 groups synperiplanar to the respective C=O bonds,and both C=O bonds synperiplanar to the O-O bond) is the only observable conformer in the vapor of the title compound. The molecule possesses a skew structure with a dihedral angle of tau(C-O-O-C) = 87.1(21)degrees. This narrow angle and the short O-O bond, 1.403(19) Angstrom, are reproduced satisfactorily by a DFT method.