Evidence of impurity accumulation in JET ELMy H-mode discharges is presented, ~10% of recent pulses included in the ELMy H-mode database being affected. ELMs lead to a peaking of the ne profile and a consequent rise in the central impurity levels. A difference in impurity behaviour is noted between pulses run with the successive divertor geometries used in JET, accumulation mainly being seen during the Mk II campaigns. This difference is understood in terms of the ne profile development and increased impurity levels. High confinement and low ELM frequency are also contributory factors to the accumulation. First transport simulations give results consistent with a neoclassical mechanism.