Microscopic traffic simulation has been successfully used in evaluation of  traffic efficiency and emissions, but not yet widely in studies of traffic  safety aspects. This paper will discuss the potential of traffic safety  simulation based on experiences from simulation studies in two research  laboratories that were using very different types of traffic simulators.  TRANSIMS (Transportation Analysis and Simulation System) is a high-speed  parallel micro simulator that allows simulation of large metropolitan areas  on microscopic level. It utilises synthetic populations to create the traffic  demand and cellular automata for high-speed parallel simulation of traffic  flows. HUTSIM is a very different kind of microscopic simulator. The  object-oriented HUTSIM model is built for very high precision simulation of  interactions between vehicles, pedestrians, traffic environment and traffic  control. Because the high fidelity of modelling requires lot of computing  power, very large networks cannot be simulated. The paper explains the  difficulties in introducing safety and behavioural aspects into existing  traffic simulation programs. The use of HUTSIM in conflict studies is  presented together with the development work carried out. TRANSIMS has been  used in the estimate of accidents in large networks and the paper presents  this work.