Massive discharge of liquid radioactive wastes into the Techa River in 1949-1956 by the industrial complex Mayak for production of plutonium for weapon resulted in protracted internal and external radiation exposure of the population living along the river. The Techa River Offspring Cohort comprises individuals born after December 31, 1949, whose one or both parents were exposed in the Techa riverside villages. The study group includes 7,897 individuals. About 40% of the Techa River Offspring Cohort members born in 1950-1956 could be exposed in utero and after birth. The mean dose estimates based on the Techa River Dosimetry System 2000 were: 0.07 Gy for parental gonads, 0.01 Gy for fetus and 0.02 Gy for postnatal exposure of bone marrow. Over 46 years of follow-up from 1950-1995, 916 subjects died and the cause of death was known in 93% of them. Out of 916 subjects dead, 456 (53%) died under 1 year of age, mainly due to respiratory tract diseases (38% of all infant deaths), infections (27%) and perinatal disorders (13%). It has been shown that the baseline infant mortality rate depends on gender, ethnicity and birth year. Radiation risk analysis was based on a simple parametric linear excess relative risk model with adjustment for gender, ethnicity and birth year. There was no evidence of increasing infant mortality risk with parental gonadal dose. The infant mortality rate significantly depended on fetal dose and dose to bone marrow received during the first year of life with a 3% increase in risk per 1 cGy of intrauterine and postnatal doses.