Historical evidence, linked with present biological evidence, can establish that the Aborigines burnt bushland in the Sydney region frequently. It also indicates that the fire regime they pursued probably varied according to the environment type being burnt, the resources they wished to extract from that environment and other reasons for burning. Using the Lane Cove valley catchment as an example (typical of the North Shore of Sydney), burning was likely to have been more frequent on the shale ridges (at 1–5 year intervals) than on the sandstone slopes (7–15 year intervals). In this area, remaining bushland is predominantly on Hawkesbury sandstone and burning at intervals more, or less, frequent than that under which it evolved leads to reduction in species diversity. Objectives must be established for the management of urban bushland and, if maintenance of biological diversity is one such objective, necessary fire regimes must be determined for individual areas and applied as a biological management tool rather than the present blanket prescription for fire hazard reduction.