The purpose of this study was to compare cortical bone thickness and density of the third metacarpal bone in horses with PPID (PPID + with pars intermedia [PI] histology scores of 4-5 / 5; n = 9), aged horses without PPID (PPID -, PI histology score < 3; n = 6), and young horses (YOUNG [ < 8 years]; n = 5).