This article presents the test setup of two quasi-static cyclic tests on U-shaped walls under horizontal diagonal loading recently performed at EPF Lausanne. The results of the first test are discussed in terms of global behaviour: failure mechanisms and force-displacement hystereses as well as in terms of local behaviour. The emphasis is placed on behaviour specific to U-shaped walls under diagonal loading, such as: 1) proneness to out-of-plane buckling of the free ends of the flanges; and 2) plane sections do not remain plane after deformation. Implications of these phenomena in the design and analysis of U-shaped walls are also discussed.