A three magnetic field component sheared plasma sheet equilibrium model is developed in the context of ideal magnetohydrodynamics (MHD). It is argued that MHD stability theory may be sufficiently correct for a thin sheet if the shear in the magnetic field is large enough. Using the model magnetic field, the ballooning eigenvalue equation is solved for several different values of equilibrium parameters. It is shown that for sufficiently large values of the shear parameter, the model is unstable to symmetric ballooning modes with a growth rate on the order of one tenth the Alfv¿n rate.¿ 1997 American Geophysical Union