The gestation period of possums is short, in comparison to other mammals. After about 17 days of gestation, the females give birth generally from May to June. Then, the newborn possum climbs to the mother's pouch, where it stays attached to a teat for about five months. One possum is born at a time in some species, such as the brush-tailed possum. Others, such as the southwestern pygmy possum, can produce litters of five to seven animals.
After five months, the young possum lives in the pouch, only returning for feeding. However, juveniles still remain very close to their mothers, frequently riding on their backs. When they are about 6 to 7 months old, possums become independent of their mothers and start to feed on insects, fruits and lives, like adults. At this time, juveniles are 7 inches to 10 inches long, weighing about 15 oz.
Although size varies across species, in most possum species adults are about the size of a domestic cat. Females generally start to breed when they reach one year of age, but this is variable according to species. Some species, such as those in the genus Cercartetus, can breed twice a year. In the wild, possums can live up to 15 years.
Some possum species, such as the eastern pygmy possum, are abundant across Australia and nearby islands. However, others are threatened of extinction, including the mountain pygmy possum (Burramys parvus), which lives in areas of alpine climate in southern Australia; Fergusson Island striped possum (Dactylopsila tatei), endemic to Papua New Guinea; and the leadbeater's possum (Gymnobelideus leadbeateri), with about 2,000 adults living in the wild.