ABSTRACT A detailed osteological description of Tyrannosaurus rex Osborn, 1905 is presented, based primarily on the most complete specimen yet collected of this taxon (FMNH PR2081, popularly known as “Sue”) but also including observations from other specimens. Skull morphology of FMNH PR2081 is largely congruent with that described for previous specimens, but new details are added. Palatal morphology of FMNH PR2081 differs slightly from that of previously-described specimens—the internal choanae are slightly larger relative to skull size, and the anterior expansion of the fused vomers is elongate. Posteriorly, the vomers pass medially for nearly the entire length of the pterygoids. High-resolution x-ray computed tomographic (CT) analysis of the skull reveals internal details not previously observed. Complex recess systems can be traced in the jugal, lacrymal, ectopterygoid, quadrate, exoccipital, supraoccipital, prootic, and basioccipital. The exoccipital recess was perforated by a small foramen on the po...