A self-consistent axisymmetric steady model of Jupiter's nightside magnetosphere is presented. Magnetospheric currents are assumed to be restricted to a thin equatorial disc and to magnetopause current sheets. The plasma velocity is assumed to be purely toroidal, and the magnetic field is assumed to be purely poloidal. Data from the Voyager missions are used as input for the solution of the equation determining the self-consistent equilibrium magnetic structure. Several numerical computations are performed, varying parameters such as the hot plasma composition and the current disc cutoff radius. We find that, with sufficiently large discs, the magnetic configuration has an X line and an O line. The X line is located between 37 and 45 Jovian radii, depending on the values chosen for the relevant parameters, while the position of the O line is less well determined. Excellent agreement between the magnetic field data in the tail and the results of the model is found. When the actual, nonaxisymmetric magnetosphere is considered, equilibrium with a purely azimuthal velocity is not possible beyond the X line, and an ordered tailward motion must develop. This could be identified either with the ''magnetospheric wind'' observed by the Voyager satellites or with the possible formation of plasmoids in the Jovain magnetosphere. ¿ American Geophysical Union 1989