Single crystal x-ray photographic data have been used to refine the structure of Sc2O3 which is isostructural with bixbyite (Fe,Mn)2O3. The average Sc3+–O2− distance is 2.11 Å, and the ratio of this value to the lattice constant 9.810 (± 0.002) Å is 0.215 equal to the analogous ratio for In2O3, the structure of which has recently been refined from single-crystal counter data. The results are compared with those on Y2O3 based on single-crystal x-ray photographic data and those obtained in the last decade by neutron and x-ray powder techniques on other sesquioxides with the bixbyite structure. Five other sesquioxides, including Y2O3, have an average M–O distance to lattice constant ratio equal to 0.215. It is probable that this is the value for all sesquioxides with this structure.