An experimental program of research was carried out to assess the potential health and safety effects of participating in virtual environments (VEs) via head-mounted displays (HMDs). This paper presents the results obtained from nine experiments examining the effects experienced during and after participation in a variety of VR systems, VE designs, and task requirements, for a total participant sample of 148 individuals. A combination of methods including self-report scales, performance measures, physiological indicators, observation, interview, and user attitude/opinion questionnaires were used to measure simulator (VE) sickness, postural instability, psychomotor control, perceptual judgment, concentration, stress, and ergonomics effects. Greatest effects across the different systems, VEs, and exposure times were found for sickness symptoms and physiological measures, with some concern over postural instability and physical ergonomics, also. Although many of the effects were relatively minor and short lived, they were serious for five percent of participants and irritating for a considerable percentage more. The aetiology of the effects is sufficiently different to that for simulators or transport systems to justify us using a new term, virtual reality-induced symptoms and effects (VRISE). Implications are drawn for VR system design, VE specification, and the ways in which industrial use of VR/VE should be planned and supported.