The article discusses content and some results of a study devoted to the integration of a geographic information system (GIS) with medical information systems (MIS). The GIS is developed upon the basis of QGIS software. The MISs used in Russian medical organizations are discovered, particularly the MISs based upon the Barclay medical database management system (Barclay DBMS). Within the study framework, a three-tier system for the medical geospatial data exchange in an integrated MIS-GIS was proposed; tools and methods were developed for data conversion and transmitting between participants involved into in the medical data management processes. The study is carried out upon data of the St. Petersburg city tuberculosis service; specialists of the SPbNIIF (St. Petersburg Research Institute of Phthisiopulmonology) and SPbCTD (St. Petersburg City Tuberculosis Dispensary) are involved in the research. Developed tools make it possible to monitor and study the spatial distribution and dynamics of of tuberculosis infection cases and concomitant diseases. The study is carried out on the scale of a large city, on the example of St. Petersburg (Russia). As a result of the work done, the implementation of GIS tools into the work of the city medical services has carried out; has ensured prompt detection and mapping of areas having maximal risk of the socially significant diseases spread; has ensured collection and representation to the user (doctor) and to the controlling persons of objective information on diseases structured not only by administrative units (districts and municipalities), but by individual houses and apartments also; the data is represented in the form of intuitive cartographic images; assistance is provided to medical specialists in the formation of an effective disease prevention system and in the identification of strong and weak elements of the disease control system.