The UO 2(001) surface has been studied by elevated-temperature scanning tunnelling microscopy (STM) and low-energy electron diffraction (LEED). The first reported STM images taken of the UO 2(001) surface reveal a maze-like structure which can be resolved atomically at negative sample bias. The observed atomic periodicity corresponds to half a monolayer of oxygen arranged in slightly relaxed (1×1) out-of-phase domains along the [110] and [1̄10] directions. The shape and arrangement of the domains causes a splitting of the LEED beams which appears as crosses in the LEED pattern. STM also allows the observation of trenches with microscopic {111} facets which may contribute to a decrease in surface energy and stabilisation of the surface.