In flight simulators simulator sickness often occurs. The main reason is believed to be conflicting sensory information. In virtual reality (VR) the average level of symptoms have been reported as approximately three times greater than in flight simulators. The main symptoms of VR sickness are nausea, disorientation, oculomotor problems, and physical strain from wearing the head mounted display (HMD). The purpose of this study was to evaluate the use of the HMD in the Air Combat Evaluation System (ACES) in respect of VR induced symptoms and strain of wearing the HMD. The effects of presenting a sideways rolling visual flow during measurements of postural stability were also investigated. This study only showed small effects of VR induced symptoms (nausea, disorientation, oculomotor) and postural instability. However, headache caused by the HMD was a considerable problem. Pain in the neck was a minor problem. The presentation of a sideways rolling visual flow increased postural instability, both before and after simulation, but did not make the measurements more sensitive to changes in postural stability after VR simulation.