The buckling capacity of steel plates stiffened with T shape stiffeners was investigated experimentally and analytically. The test specimens, 2000 mm long, were fabricated with a 500 10 mm plate stiffened with a WT 125 12.5 stiffener. The experimental program was designed to investigate the effect of unloaded edges boundary restraint, combination of in-plane and out-of-plane load, and imposed plate damage on the buckling capacity of stiffened steel plates. The residual stresses were measured in a representative test specimen and initial imperfections were measured for each test specimen. The residual stresses and the measured initial imperfections were included in the finite element model. A large deformation and finite strain analysis was performed using the finite element code ABAQUS. The finite element analysis was found to predict very accurately both the behaviour and capacity of stiffened steel plate panels. Stiffener tripping and plate buckling modes were equally well predicted.