A simulation of the fire at Montagnac (Gard - France) was performed with a random, chaotic model designed in 1987 and then developed later to demonstrate that it is easy to simulate a fire in realistic manner but had never been parameterised using real cases. The demonstration model was therefore parameterised a posteriori and modified to make it automatic for the zone processed. The initial point was set near the place of outbreak of the real fire, wind speed and direction were set and constant and all interactive functions were removed and especially those simulating control facilities. The successive simulations displayed on the computer monitor show that: movement of the fire is generally adequately represented in the wooded part with no obstacles; however, the various perimeters shown may differ from each other substantially, as may the areas covered (these differences are mainly random); progress of the fire is only adequately represented in the terminal zone if all the obstacles are crossed simultaneously; if not, the variations are substantial and chaotic.