Gas-phase electron diffraction data at 23°C together with molecular mechanics (MM3) and ab initio (HF/6-31G * ,gaussian 86 ) calculations have been used to determine the structure and conformations of 1,4-difluorobutane. The object was to ascertain whether effects similar to the gauche effect in 1,2-difluoroethane, which serves to stabilize the gauche form with the fluorine atoms in close proximity, could also operate in 1,4-difluorobutane. It was found both theoretically and experimentally that the proportion of those conformers having close fluorine atoms was small, implying the absence of effects similar to the gauche effect. The conformational composition estimated from the theoretical calculations is in good agreement with the experimental data. The experimental electron diffraction results constrained by assumptions drawn from the theoretical calculations, ED/MM3 [ED/ab initio], for the principal distances (r g / ) and angles ( α /deg) with estimated 2σ uncertainties are as follows: r(C-H) = 1.105(3) [1.106(3)], r(C-F) = 1.398(2) [1.398(2)],r (C 1 -C 2 ) = 1.513(2) [1.516(2)], r(C 2 -C 3 ) = 1.537(2) [1.532(2)], F-C-C = 110.9(3) [111.1(3)], C-C-C = 112.9(4) [112.9(4)], and H-C-H = 100(3) [100(3)].