Organization of the RSMDR System. The Russian State Medical-Dosimetric Register of individuals subjected to radiation as a result of the Chernobyl accident (RSMDR) was created in 1986. The head organization the state level of RSMDR is located in the Medical Radiological Scientific Center in Obninsk. The main objective of RSMDR is to maintain an automated long-time list of individuals subjected to radiation as a result of the Chernobyl accident, their children and subsequent generations, the irradiation doses, and assessment of the state of health and its changes for the purpose of making optimal decisions so as to minimize the medical consequences. The RSMDR is a multilevel information system which encompasses the Russian Federation [1]. Interregional centers for collection of medical-dosimetric information, acquired from regions and provinces, and subsequent transfer of this information to the state level have been created in all eleven economic regions. Besides the interprovince regional centers, created on the territorial principle, the RSMDR has centers in the Ministries of Defense, Internal Affairs, Communication, Atomic Energy, and FSK. Branches which have the status of regional centers have also been created in Bryansk, Kaluga, Tul, and Orl, i.e. in provinces whose population experienced the greatest irradiation. All centers of RSMDR are equipped with modern personal computers and are staffed with qualified specialists in information science, medicine, radiation epidemiology, and dosimetry. A unique bank of medical-dosimetric information and an analytical system for predicting radiation effects have been created at the state level of the RSMDR. These systems have no analogs in worldwide practice in the investigations of the consequences of radiation catastrophes. General Information. According to Fig. 1, the data bank for the state level of the RSMDR is filled continuously with medical-dosimetric information and now includes 324,146 people. All individuals registered in the RSMDR system are divided into four groups: participants in the liquidation of the consequences, evacuated individuals, individuals who lived in the observed territories, and children born to the participants in the liquidation of the consequences in 1986-1987. Many registered individuals are from central and northern Caucasus regions of Russia. In the central region most individuals lived in the observed territories of the Bryansk, Kaluga, Tul, and Orlov regions and in the northern Caucasus region they were participants in the liquidation of the consequences. Dosimetrie Data on the Cohorts of the Participants in the Liquidation of the Consequences of the Accident. The most accurate and verified medical-dosimetric data in the RSMDR pertains to the individuals who participated in the liquidation of the consequences. Data on the irradiation loads come from official documents, released to participants in the liquidation of the consequences after performing work in zones of radioactive contamination. The irradiation dose indicated in the documents is recorded by an individual or group dosimeter or estimated according to the time spent doing the work taking into account the radiation conditions in this zone and along the path to it. We established the geographic coordinates of the populated points, where the participants in the liquidation of the consequences lived or worked. Analysis of the data showed that most individuals worked in a 100-kin zone around the Chernobyl nuclear power plant. A large fraction of the participants in the liquidation of the consequences of the accident in 1987-1989 worked outside the 30-krn zone. For statistical analysis of data on the absorbed dose of external irradiation by T emitting nuclides, 119,416 records were selected from the RSMDR database for which the populated points where work was performed were determined and for which the dose did not exceed 50 cGy (if the dose was indicated in roentgens in the RSMDR document, then before the data were verified, which is now being done, the dose was not converted to absorbed-dose units). Data on the doses exceeding 50 cGy (approximately 300 records) are now being verified.