The fortuitous timing of the Voyager 2 flyby of Neptune provided a unique opportunity to carry out plasma and magnetic field measurements in a subsolar cusp region of a planet. The measured plasma parameters near the inbound magnetopause strongly suggest that a rotational discontinuity separates the magnetosheath and the high-altitude cusp region. After crossing the magnetopause, a thick layer of magnetosheathlike plasma was observed which can be accounted for by two models: (1) either a cusplike layer of stagnant plasma separated from the magnetosheath by a tangential discontinuity, or (2) or a mantlelike layer of dynamic plasma separated from the sheath by a rotational discontinuity. The plasma observations are more consistent with the mantle interpretation. Distinguishing the mantle and the stagnant cusp models is not possible on geometrical grounds because Voyager 2 crossed the magnetic polar region on the subsolar side. Inside the cusp region, there is an overall decrease in the ion density and a concurrent increase in the magnetic field strength which is consistent with a slow mode expansion fan such as is encountered in Earth's polar regions. ¿American Geophysical Union 1991