The purpose of this article is to analyze changes in the diagnosis of causes of death of the local population and to study the relationship of these changes with the development of medicine and unification of the definition of causes of death in Russia. The information base of the study is the registers of the two parishes in the Moscow County in the period from 1815 to 1918. The obtained results show a significant improvement in the diagnosing of causes of death in the second half of the XIX century, connected with the expansion of the network of medical institutions in the Moscow Province and the activity of the medical society in the development of the Russian nomenclature of diseases.