This paper describes the survival rates of 763 rhesus monkeys maintained at the Yerkes Regional Primate Research Center (YRPRC). The survival rates were determined by methods used to calculate survival rates of human populations. The monkeys were divided into 3 groups based on their specific life histories. Group I monkeys were wild-born and were housed singly from the time they came into captivity at about 2 years of age. Group II monkeys were born either in the wild or in captivity and were housed in social groups since their acquisition at ages 2 to 8 years. Group III monkeys were born at the YRPRC and housed in social groups. Due to these differences in life histories, direct comparisons among survival curves of the 3 groups are, at best, tenuous, as are comparisons with populations maintained at other facilities. In the present study the highest mortality rate occurred during the first month of life. The maximum life span attained in our group I was 35 years, with only 6.2% of monkeys in this group attaining an age beyond 30 years.