The study of syphilitic infection in the human being involves the following up of patients' conditions over long periods of time. The clinic is in many ways analogous to the experimental laboratory; the patient can sometimes tell one as much as the examination of a rabbit shows, even though a planned experiment is harder to achieve. A large amount of clinical material, no matter how carefully the patients are followed, is, however, of little value for study and research purposes unless it can be readily classified and made available to the investigator. The diagnosis file in use in the Syphilis Clinic of the Johns Hopkins Hospital has proved to be of so much service in this respect that I am publishing a general outline of it, with the thought that it may be of equal value, subject to local modification, to other clinics handling large numbers of patients with syphilis.