The room temp. phase of the B-site disordered perovskite Pb(Fe0.5Ta0.5)O3 (PFT) was studied by single crystal x-ray diffraction and by polarized light microscopy. While pyramidal (100) growth sectors display a weak birefringence, indicating a tetragonal symmetry with an optically uniaxial pos. indicatrix, the structure of PFT crystals can be well refined in cubic space group Pm.hivin.3m, however, the introduction of disorder on the A site is necessary. In the light of the optical symmetry, the (x00) A-site disordered cubic structure was considered as a mean structure averaged over tetragonal domains, each contg. Pb displaced just towards one of the three [100]cub equiv. directions. Attempts at refinements in tetragonal symmetry and at mech. (ferroelastic) switching of domains are discussed.