Although a substantial backyard might be considered an iconic Australian feature, by the late 1990s, almost all new suburban houses had minimal provision of soft-landscaped private open space. This article presents results of research that has investigated important aspects of this phenomenon. It has measured the changes on a sample basis and has attempted to relate the changes to their planning policy context. The environmental significance has been assessed in relation to the literature. Quantitative analyses of examples from older and newer suburban form are presented. They indicate that this is happening irrespective of size of lot and appears connected with a trend to larger dwellings in relation to the lot area. It represents a loss that has serious ecological implications for the community as a whole, including a significant reduction in biodiversity, sustainable drainage and a beneficent microclimate, in addition to lower standards of domestic amenity. It does not appear that the reduction in size is being required by planning policies. Planning codes, while not actually encouraging the trend, do nothing to prevent it. The phenomenon is to be found even under progressive planning regimes and in nearly all master-planned estates.