A measurement of the top-antitop t t ¯ charge asymmetry is presented using data corresponding to an integrated luminosity of 4.6 fb −1 of LHC pp collisions at a centreof-mass energy of 7 TeV collected by the ATLAS detector. Events with two charged leptons, at least two jets and large missing transverse momentum are selected. Two observables are studied: A C ℓℓ based on the identified charged leptons, and A C t t ¯ , based on the reconstructed tt final state. The asymmetries are measured to be A C ℓ ℓ = 0.024 ± 0.015 stat . ± 0.009 syst . , A C t t ¯ = 0.021 ± 0.025 stat . ± 0.017 syst . .