BACKGROUND: In the 19th century, the process of annexation of lands in the north-east of the Russian Empire was completed. The influx of newcomers, political exile, criminal hard labor created the prerequisites for an aggravation of the epidemiological situation in the newly annexed territories. The morbidity of the population began to acquire an epidemic character. Syphilis, which spread in the 19th century, leprosy struck foreign communities in the northern and eastern regions of the Pacific Ocean, the Sea of Okhotsk, the Kamchatka Peninsula and the alien population from other territories.
 AIM: Systematize, as well as identify certain trends in the prevalence and forms of manifestation of syphilis and leprosy among the population of the north-eastern districts of Eastern Siberia of the 19th century. according to the reporting materials of doctors and authorities of that time. Let us explain: in this article, the authors quote from the documents, preserving (if possible) the style and punctuation of the originals, and also use geographical names and names of territories adopted in the Russian Empire in the 19th century.
 MATERIALS AND METHODS: On the basis of archival materials, the article discusses the ways of importation and spread of syphilis among representatives of individual foreign communities, the clinical course and forms of manifestation. The multiplicity of ways of penetration of syphilis to the outskirts of Eastern Siberia is noted. The reports of seconded staff physicians, doctors, paramedics during the examination of the population and the treatment of patients in hospitals provide the first statistical information on the incidence of men, women, their nationality, and the outcome of treatment. The reports of seconded staff physicians, doctors, paramedics during the examination of the population and the treatment of patients in hospitals provide the first statistical information on the incidence of men, women, their nationality, and the outcome of treatment.
 RESULTS: The article highlights the issues of studying the role of factors contributing to a high level of the spread of syphilis and leprosy among inorodtsy (indigenous dwellers), describes the symptoms of manifestation, and especially chronic syphilis, and notes the role of unsanitary living conditions and household arrangements in the spread of diseases.
 CONCLUSIONS: Observation of the clinical manifestations of syphilis allowed doctors to isolate leprosy as an independent form of the disease, and to investigate its causes. These observations were the basis for the development of measures aimed at stopping the spread of the disease among the population. The beginning of the emergence of medical and police supervision aimed at identifying patients, registering them and treating them is noted.