Most of the volatile haloorganic compounds used as anesthetics exhibit a heavy-atom frame large enough to allow for conformational changes. Even in the absence of directed intermolecular interactions, only some or just one of the possible conformations might have an appreciable abundance. In this realm, the structure of the anesthetic haloether sevoflurane (CH(2)F-O-CH(CF(3))(2)) has been resolved using Fourier-transform microwave (FT-MW) spectroscopy in a supersonic-jet expansion. In isolated conditions sevoflurane adopts a single conformation characterized by a gauche fluoromethoxy group and a near-symmetric orientation of the isopropyl group with respect to the ether plane (cis H-C(ipr)-O-C(F)). Substitution and effective structures have been calculated from the rotational spectra of all (13)C and (18)O monosubstituted isotopic species observed in natural abundance. The electric dipole moment components were determined from additional Stark effect measurements. The experimental structures and rotational data are compared with those obtained from supporting ab initio predictions using MP2 calculations and the B3LYP hybrid functional.