Three high. temperature structural phase transitions have been identified in the perovskite-structured phase SrSnO3 using differential scanning calorimetry and dilatometry, and have subsequently been structurally characterised using high resolution neutron powder diffraction. Between 298 and 905 K, SrSnO3 is orthorhombic, space group Pmcn, before undergoing a continuous phase transition to a second orthorhombic phase in space group Incn. At 1062 K there is a first order phase transition to a tetragonal phase in space group I4/mcm before finally transforming-to the aristotype phase at 1295 K. Using the magnitude of the anti-phase tilt as a measure of the order parameter-for-the transition,from I4/mcm to Pm3m suggests this transition is tricritical in nature. Crystal structures are reported for the three hettotype phases. (c) 2004 Elsevier Ltd. All rights reserved.