Simulator sickness has been identified as a form of motion sickness in which users of simulators exhibit symptoms characteristic of true motion sickness. In a fixed-base simulator, visual and vestibular sources of information specifying dynamic orientation are in conflict to the extent that the optical flow pattern viewed by the pilot creates a compelling illusion of self-motion, which is not corroborated by the inertial forces transmitted through the vestibular sense organs. Visually induced illusory self-motion is known as vection, and a strict interpretation of sensory conflict theory of motion sickness suggests that vection in a fixed-base simulator would be a necessary precondition for simulator sickness. Direct confirmation of this relation is reported in this article.