The population ecology of the sugar glider, Petaurus breviceps, was examined during a 31-month capture-mark-recapture study in a 20-ha system of remnant native vegetation in farmland. Overall population densities ranged from 6.1 ha- 1 in autumn to 2.9 ha- 1 in summer. However, the various areas composing the system had different management histories and were found to contain varying densities of P. breviceps. Differences in density were most readily explained by differences in abundance of black wattles, Acacia mearnsii, which provided an important autumn and winter food source. At least 75% of animals lived in groups containing up to seven adults from up to four age-classes (usually three males and four females). There was a single breeding season beginning in late winter or early spring each year; at least 80% of female P. breviceps surviving to the breeding season following their birth produced young, and almost all adult females in other age classes bred in any year. Of all litters born in the study site, 81% were twins, and the remainder were of single young. The overall mean litter size was 1.8. Up to 50% of all offspring left their group of origin by the beginning of the breeding season following their birth, though some older gliders. apparently unattached to any group, also dispersed. A roadside strip of forest, between one and four trees wide, was found to facilitate dispersal into a vacant habitat within the system studied.