Nuclear bomb testing was carried out under conditions of secrecy at the Semipalatinsk test site (STS) between 1949 and 1962. The first test on August 29, 1949 unexpectedly contaminated villages to the northeast, both in Kazakhstan and the Altai region of Russian Siberia. In Kazakhstan, extensive measurements were made of fallout concentration on the ground and there were efforts, which were not always successful, to avoid future fallout contamination of population centers. As soon as evidence appeared of excess leukemia risk among the survivors of the atomic bombings of Hiroshima and Nagasaki and among medically exposed populations, attention turned to potential health consequences in the population near the STS. In 1957, a secret medical institution, specializing in oncology and designated 'Dispensary Number 4', was established in Semipalatinsk to perform diagnostic and clinical ward, to collect data on the population's health status in the Semipalatinsk oblast, and to collect various material for possible future analysis. The Kazakh Research Institute for Radiation Medicine and Ecology (KRIRME), which was founded in 1991, inherited the functions and the formerly top secret health archives of Dispensary No. 4. These archival data including the information on the KRIRME study population of residents of heavily exposed and less exposed villages in the oblast, are the basis for a number of international collaborative projects focussed on fallout exposure and possible health effects in the exposed population.