The northern quoll Dasyurus hallucatus is a sexually dimorphic carnivorous marsupial found in northern Australia. Despite males weighing up to 1120 g, in at least some populations all males die after mating. Radio-tracking and live-trapping at a lowland savanna site in Kakadu National Park indicated that females occupied home ranges averaging 35 ha with intra-sexually exclusive denning areas. There was some overlap of foraging ranges when the density was 3–4 females/km2, but no overlap during periods of lower population density (1–2 females/km2). Male home-range size may be similar to females before the mating season, but expands during the mating season to > 100 ha to overlap extensively with several female ranges and numerous other male ranges. Despite this range overlap, both sexes were solitary. Even during the mating period, males denned on average 0.27 km from females during the day. During the mating period, each female was visited by at least one to four males per night. During this period, the increase in scat deposition in prominent positions in the landscape and the simultaneous increase in sternal gland activity of the males suggest the importance of olfactory communication to advertise the presence and sexual status of individuals. Males adopted a roving strategy, regularly visiting several widely spaced females in rapid succession, presumably to monitor the onset of oestrus. This intense physical effort during the mating period is likely to be a major contributor to the physiological decline of the males and subsequent die-off after the mating period. The marked sexual dimorphism of D. hallucatus may be the result of selection for larger, wider-ranging males in a promiscuous mating system and for energetically efficient smaller females, as females rear the young alone.