It is widely believed that with the LHC start up a plethora of new physics signals will become accessible experimentally, with a whole new rich phenomenology expected to be observed at ATLAS in the first years of data taking. Supersymmetry (SUSY) provides one of the most accredited and exciting theoretical frameworks which can be used to extend the Standard Model of particle physics to the vastly unexplored territory at the TeV scale. Besides the typical inclusive SUSY signatures with high-pt multi-jets and large transverse missing energy, and possibly one high-pt lepton, a very clean SUSY signal is expected to be observed in the channel with three leptons in the final state, which can for example arise from gaugino and slepton decays in dark matter relevant regions of the parameter space.