Abstract : Distance judgments in virtual environments and Head-mounted Displays (HMD) systems are generally underestimated compared with judgments in the real world. Some visual depth cues may be absent or modified, according to the technology used. After a brief review of the literature pertaining to the representation of depth in Helmet-Mounted Displays, we explore two possible causes for the reduced distance perception in virtual environments: the increased interocular separation (or hyperstereopsis) and the reduction of the field of view. Some laboratory and training ground data are reported. The effective influence of each factor on space perception is discussed.