  We have used high precision differential astrometry from the Palomar
High-precision Astrometric Search for Exoplanet Systems (PHASES) project and
radial velocity measurements covering a time-span of 20 years to determine the
orbital parameters of the 88 Tau A system. 88 Tau is a complex hierarchical
multiple system comprising a total of six stars; we have studied the brightest
4, consisting of two short-period pairs orbiting each other with an 18-year
period. We present the first orbital solution for one of the short-period
pairs, and determine the masses of the components and distance to the system to
the level of a few percent. In addition, our astrometric measurements allow us
to make the first determination of the mutual inclinations of the orbits. We
find that the sub-systems are not coplanar.
