Abstract : One challenging human factors issue in Helmet-Mounted Displays is the alteration of perceived distance. Distances judgments in virtual environments and Helmet-Mounted Displays are generally underestimated compared to the real world. Indeed, visual stimulation in Helmet-Mounted Displays presents some discrepancy with natural visual stimulation. After a brief review of the literature pertaining to the representation of space in Helmet-Mounted Displays, we explore two potential factors for the altered distance perception: the increased interocular separation (also called hyperstereopsis) and the reduction of the field of view. Some laboratory and training ground data are reported. This research has direct impact on the design and use of Helmet-Mounted Displays in order to ensure flight safety.