The geometric structure and the conformational composition of 1,1,1-trifluoromethanesulfenylamine, CF3SNH2, were investigated by gas electron diffraction (GED) and microwave spectroscopy (MW). In the MW spectra transitions of two conformers were observed. Rotational constants of deuterated species demonstrated that the more intense transitions belong to the anti form (nitrogen lone pair antiperiplanar to S–C bond). From relative intensities and dipole moments an energy difference ΔE=E(syn)−E(anti)=1.1(1)kcalmol−1 was derived. A joint analysis of GED and MW data resulted in the following skeletal parameters (rz values with 2σ uncertainties): S–N=1.673(5)Å, S–C=1.836(5)Å and C–S–N=101.8(8)°. These parameters and the energy difference are well reproduced by B3PW91/6-31G* calculations.