The evolution of them&thgr;=1 diocotron mode for hollow density profiles has been an open problem of non‐neutral plasma physics for more than a decade. In fact, the classic 2D fluid model leads to results that are in substantial disagreement with the ones provided by experiments. In the present work, a simplified kinetic model is proposed, in order to provide a quantitative estimate of the role played by kinetic effects on the evolution of the m&thgr;=1 diocotron instability. A two‐fluid model is deduced and a linear analysis of stability is performed, showing that kinetic effects can play an important part in the description of the evolution of them&thgr;=1 diocotron mode. © 2003 American Institute of Physics