The tiger quoll or spotted-tailed quoll Dasyurus maculatus, a nationally threatened species, is the largest surviving carnivorous marsupial on mainland Australia and the sole surviving member of the genus in south-eastern mainland Australia. Live-trapping and radio-tracking studies at three sites in south-eastern Australia found that tiger quolls were solitary, except when mating, and that male and female tiger quolls occupied very large home ranges, both during and after the breeding season. The mean size of the home range of male tiger quolls (minimum convex polygon (MCP) 1755.4 ha, kernel 3761.7 ha) was significantly larger than the mean size of the home range of females (MCP 495.9 ha, kernel 1113.0 ha). Adult female tiger quolls displayed intrasexual territoriality throughout the year, but they seemed to tolerate the presence of female offspring. Male tiger quolls were not territorial and their home ranges overlapped both with other males and with females throughout the year. Males were recorded regularly moving back and forth between a number of female territories during the breeding season. The spatial organization of the tiger quoll recorded in this study differs markedly from that of the eastern quoll Dasyurus viverrinus and the Tasmanian devil Sarcophilus harrisii, but is similar to that of the western quoll D. geoffroii, northern quoll D. hallucatus and brush-tailed phascogale Phascogale tapoatafa. The spatial organization and home-range size of the tiger quoll dictate that conservation of the species requires management across all land tenures at the landscape level.