AbstractAn ecological comparison, with special reference to tropical affinities, is made between the rain forests of New Zealand and south‐east Australia, based on the distribution of seventy physiognomic‐structural attributes in mature forests at selected sites (ten in New Zealand, twenty in Australia, and four in New Guinea to represent authentic humid tropical lowland rain forest). The structural data were recorded in a standardpro formaand subjected to classification, ordination and two‐parameter analysis.In the classification, the Australian and New Zealand sites, with two exceptions, separated at the four‐group level. The more complex (cool subtropical) Australian types were the least related to the New Zealand forests, which are closest to Australian simple (submontane) types. There was a similar distinction in the ordination, in which the trend along the first two vectors was latitudinal, correlated with extremes of temperature and with moisture availability.The relative contributions of the structural attributes to the various site groupings in the classification and ordination are enumerated, and provide an objective scale of comparison of the forests. Structural attributes designated by analysis as exclusively or preferentially tropical by reference to the New Guinea sites are then used to assess degree of tropical affinity.The simplified cool temperate (montane) forests dominated by one species ofNotho‐fagusin New Zealand and Australia are closely related. The Australian forests of the sub‐montane zone (mean annual temperature 12–15° C) which are typically dominated by Ceratopetalum apetalum, Nothofagus mooreiorDoryphora sassafras, are similar to the podocarp‐broadleaf forests, with or without kauri, of New Zealand. The Australian forests of the cool subtropical zone (mean annual temperature 15–17°C) which have mixed dominants, have some affinities with the kauri‐podocarp‐broadleaf forests of North Auckland. In New Zealand, a broadleaf type in which kauri is absent or rare on basalt in North Auckland (lat. 35° S) was the most complex forest sampled and i