Spatial dysgnosia may occur in patients with various forms of brain disease, including tumors, vascular accidents, Alzheimer's disease, multiple sclerosis, and developmental aberrations. Patients with lesion in the nondominant hemisphere, particularly at the junction of the occipito-temporoparietal regions, may manifest predominantly visuospatial dysgnosia--a loss of the sense of "whereness" in the relation of himself to his environment and in the relation of objects to each other. Visuospatial disturbances caused by lesions in the dominant hemisphere may be masked by other gnostic symptoms. Patients with more extensive lesions, especially those involving similar areas in both hemispheres, may also exhibit other cognitive disturbances associated with vision.