The eastern pygmy-possum (Cercartetus nanus) has posed a challenge in attempts to describe its population density due to low rates of capture, preference for patchy habitats and periodic influxes of subadult individuals. We conducted a mark–recapture study of this species using a grid of nest boxes in a 9-ha patch of banksia heath–woodland. We captured 54 adults across the two years of our study. We estimated the density of adult pygmy-possums to be 1.5–4.2 ha^–1 from different population models. This is substantially lower than previous estimates in equivalent habitat because we focussed on adults and recognised that they were not confined to the area bounded by our grid. We captured 36 subadults over the two years but they could not be reliably modelled due to extremely low recapture rates, which reflect high rates of dispersal and also mortality. For this reason, only the number of adults should be used to characterise populations of this species. Further study is required to investigate population dynamics over time and to describe the density of eastern pygmy-possums in other habitats.