The Cornell Medical Index-Health Questionnaire is a self-administered instrument that collects a large body of significant medical and psychiatric data without the physician's participation, so that the physician may have available, even before he interviews the patient, information on which to base tentative diagnostic appraisals of the patient's total medical problem. This communication reports the accuracy and completeness of the diagnostic appraisals that can be made with the data on the Cornell Medical Index. DESCRIPTION OF THE CORNELL MEDICAL INDEX The Cornell Medical Index-Health Questionnaire (C.M.I.) is a four-page, letter-size sheet on which are printed 195 questions corresponding closely to those usually asked in a detailed and comprehensive medical interview.1 Many questions on the psychological aspects of medical disorders are included. Questions are in informal language and worded to be understood by persons with a reading knowledge of simple English.