Animal experiment findings suggest that high doses of ionizing radiation exposure (>1.0 Gy) may cause genetic and epigenetic effects in offspring. However, epidemiological studies of offspring of radiation-exposed parents did not find increased risks of any health effects. Findings of cellular/experimental investigations and studies of human health effects are contradicting, and further investigations are needed to help resolve ambiguities using updated and/or improved data. This paper provides a detailed description of a database of families of workers of the first Russian nuclear facility, Mayak Production Association, located in the Southern Urals in the Chelyabinsk region close to Ozyorsk city, which started its operation in 1948 and today consists of reactors, radiochemical and plutonium production plants, and auxiliary facilities. The Mayak worker cohort includes 22,377 individuals (25% females) who were hired at one of the main Mayak PA facilities between 1948 and 1982 and were externally or internally exposed to ionizing radiation over prolonged periods. Advantages of the cohort include its large size, extensive follow-up period (70 y), individually measured doses from external and internal exposure and the wide range of these doses, heterogeneity by gender/age/ethnicity/initial health status, complete data on vital status and causes of death, available medical information on morbidity and reproduction, available data on non-radiation factors, and stored biological specimens donated by more than one-third of the cohort members. Based on medical and dosimetry database “Clinics” containing raw data on workers of the study cohort, the Mayak workers’ family and offspring database was created. To date, it comprises 12,195 family couples (a husband and a wife) and 16,585 offspring. Biological specimens are available for more than 1,000 family triads (a husband, a wife, and their child). Stages of assembling the database and its descriptive characteristics are presented in this paper. Examples of potential applications of the database for investigations of non-targeted and transgenerational radiation effects in offspring of exposed parents are discussed.