The structure of tris(pentafluoroethyl)phosphane, P(C(2)F(5))(3), has been determined in the solid state by in situ single crystal growth and subsequent X-ray diffraction and in the gas phase by electron diffraction. The experimental structure determinations have been supported by and compared to quantum chemical calculations at different levels of theory. P(C(2)F(5))(3) prefers a conformation of C(3) symmetry with the CF(3) groups of the three C(2)F(5) units oriented to the same side of the molecule as the phosphorus lone pair of electrons, leading to an estimated Tolman cone angle of 193 degrees (solid) and 191 degrees (gas), whereas a second stable conformer of C(3) symmetry, (only 5 kJ mol(-1) higher in energy) has a smaller Tolman cone angle of 171 degrees . The structures are discussed in context with related molecules E(CF(3))(3) (E = N, P, As, Sb) as well as N(C(2)F(5))(3) and P(C(2)H(5))(3).