Of full-term births in a colony of S. o. oedipus, 43% occurred during April and May. Interbirth interval was usually 12 mo. in females which reared live young and 7 mo. in those whose young died perinatally. Of all full-term births, 81% were of twins, the rest were singles. High mortality among neonates was seen with a group of bought-in animals which had been taken from their parents at an early age without participating in the rearing of siblings, and was attributable to parental incompetence. Colony management aiming to ensure that animals gain experience in caring for young before breeding is described. Mortality among all animals older than 7 days was very low. Marginal protein deficiency may have been involved in a chronic diarrhoea and weight loss syndrome seen in some animals. They recovered after addition of hard-boiled egg to the diet.