The crystal structures adopted by BaPrO3 at and above ambient temperature have been examined using a combination of synchrotron X-ray and neutron diffraction. BaPrO3 has been established to undergo a series of phase transitions from Pbnm orthorhombic -> Ibmm orthorhombic -> R (3) over barc rhombohedral -> Pm (3) over barm cubic. BaPrO3 is the second A(2+)B(4+)O(3) perovskite found to adopt rhombohedral symmetry in preference to the 14/mcm tetragonal structure. Analysis of the octahedral tilting through the rhombohedral to cubic phase transition indicates that this transformation is continuous and tricritical in nature. The tricritical behaviour of this transition is likely to be a result of the competition between tetragonal and rhombohedral structures to be the preferred phase, with the rhombohedral symmetry adopted by BaPrO3 being stabilised by the unusually large B-site cation. (C) 2008 Elsevier Ltd. All rights reserved.