The development of modern gas turbine combustors is linked to the goal of low NOx emissions. Low NOx Gas Turbine (LNGT) combustors operate at lean conditions, thus ensuring low flame temperature, and are, then, adequate to accomplish this requirement. Unfortunately at lean conditions, just before blow-out, spontaneous oscillations of pressure and temperature can be observed [1-4]. These oscillations are unwanted as they cause acoustic oscillations and mechanical and thermal stresses which can damage the combustor and the engine. In order to understand the mechanisms which drive the instabilities in lean premixed combustion, many studies, both experimental and theoretical, were carried out, but up to now it is still unclear if the occurrence of the oscillations has to be related to instability of the flame (intrinsic instabilities), or whether there is a feedback mechanism between acoustics and heat release from the flame (system instabilities). The intrinsic instabilities may have different origins: intrinsic kinetic instability [5, 6], thermal-diffusion instability and hydrodynamic instability [7, 8]. Many authors relate the observed oscillations to system instabilities and more precisely to the coupling between the oscillating heat produced by the chemical reaction and the acoustics [2- 4, 9-12]. The heat release is assumed to oscillate due to the periodic variations of the air and/or fuel flow rates and, then, of the equivalence ratio. Most of these models are zerodimensional or 1D and do not show spontaneous oscillations: they assume that the pressure field is oscillating and coupled with the heat release due to the reaction. Consequently, it is still unclear what is exciting the oscillating mode. Spontaneous oscillations were simulated by means of multidimensional models, in which coupling between combustion and fluid-flow is taken into account. This occurrence was addressed to the unsteady heat release at the flame front, which can be in phase with the acoustic resonance of the system, depending on the distance between fuel injector and flame zone [9-11]. In a previous paper [13] we showed, according to the experimental results of Richards et al. [1], that combustion of lean mixtures may give rise to spontaneous oscillations near the blowout points. The dynamic features of lean premixed combustion were studied by modelling the combustion zone as perfectly mixed and the stability analysis was performed by means of the bifurcation analysis. The satisfactory comparison between the experiments and the theoretical results allowed us to illustrate that the origin of the oscillating behaviour can be thermokinetic, i.e. related to the coupling between the stabilising effect of heat produced by chemical reaction and the destabilising effect of heat losses, enhanced at lean conditions. This represents an intrinsic instability rather than a system instability. The simplified model adopted was able to point out the genesis of the dynamic regimes, but it was unable to take into account any effect of coupling with the fluid flow and spatial non uniformities. With the specific purpose of confirming the previous analysis in a realistic configuration, in this paper we present the results of CFD simulations showing the dependence of the dynamic behaviour of a lean premixed combustor on the presence of heat losses.