summary.-This paper provides a description of the cerebellar-vestibular determined (CV) neurological and electronystagmographic (ENG) parameters charac terizing 4,000 patients with learning disabilities. Of this sample, 1465 or 36.6% were children, 1156 or 28.9% adolescents, and 1379 or 34.5% adults. Using a set of diag nostic methods and criteria, the incidence of CV-dysfunction in this diverse sample was statistically equivalent to that reported by neurologists and neurotologists in a prior "blind" analysis of 115 dyslexic children. Over 94% of both the learning dis abled and the dyslexic samples showed two or more abnormal neurological or ENG parameters indicating a CV-dysfunction whereas less than 1% evidenced hard neuro logical signs of a cerebral disorder. These and related data suggested that: (l) learning disabilities and dyslexia may be cerebellar-vestibular-based and reflect a single disor der and that (2) the varying academic, speech, concentration, activity, and related symptoms characterizing learning disabled persons seem to be shaped by a diverse group of cerebellar-vestibular-determining mechanisms rather than distinct neurophysi ological disorders; also, (3) cerebellar-vestibular dysfunctioning and learning disabilities may secondarily trigger altered and/or compensatory cerebral processing and dominance mechanisms. (4) The cerebral cortex apparently plays a vital, compen satory role in shaping the final symptoms. A cerebellar-vestibular basis of learning disabilities is proposed. This conceptualization is consistent with, encompasses, and/or readily explains most of these clinical diagnostic, therapeutic, and research data as well as the many and varied hypotheses.