An exact observer approach for simultaneous state and parameter estimation is proposed for the well-known van der Pol oscillator. The approach is based on an appropriate state space representation - using the so-called Lienard transformation - allowing for an exact Kalman-like observer design. The stability is then formally checked relying on the natural oscillatory behaviour of the system, and the corresponding results are illustrated in simulation. (C) 2010 Elsevier Ltd. All rights reserved.