The cynomolgus monkey is widely used in reproductive research. However, the effects on their reproductive parameters of infant and maternal factors such as birth order, sex of infants, twin births, maternal age and lactation status have not been fully examined. The aim of this retrospective study was to determine how such infant and maternal factors impact on infant birth weight, birth viability, neonatal loss and retained placenta in cynomolgus monkeys. The study was based on birth data from a cohort of 789 females over an eight-year period. Consistent with reports made in other macaque species, female offspring had lower birth weight compared with males. Birth weights of firstborn infants were lower compared with birth weights of higher birth order infants. Results from the logistic regression analysis showed that the risk of non-viable births was increased by advancing maternal age and retained placenta. As in other non-human primates, maternal age had predictive value for non-viable births in cynomolgus monkeys. The risk of neonatal loss decreased with advancing maternal age but was not affected by birth order. Firstborn offspring did not have an increased risk for neonatal loss, possibly from the practice of retaining mothers in their natal groups, which improved maternal skills in primiparous females. However, infant low birth weight and non-lactating females increased the risk of neonatal loss, and the delivery of low birth weight infants was associated with retained placenta. The results from this study can be useful for scientists conducting reproductive studies and for colony managers in maximizing fertility and infant survival of cynomolgus monkeys.