This paper presents the results of a study carried out to determine the drained stress–strain behaviour of a sensitive clay from St-Louis de Bonsecours (Quebec), tested under conventional axisymmetric (σ′1 > σ′2 = σ′3) and complex true-triaxial (σ′1 ≠ σ′2 ≠ σ′3) stress states.The data reported herein show that, for confining pressures below the preconsolidation pressure of the clay, the influence of cementation bonds and anisotropy results in deviation from the Mohr–Coulomb theory and causes the clay to behave as an anisotropic pseudo-elastic, plastic material. It is shown that constitutive relationships derived from the theories of anisotropic elasticity and plasticity represent very well the mechanical response of the clay.