The distribution of play behaviour among the Australian marsupial families was surveyed. The rate of play in each species observed was categorized on a three-point scale: 1 – no play observed or reported; 2 – play rudimentary; 3 – play common. Common play occurred in the larger-bodied Dasyuridae, in Myrmecobiius, in Vombatidae, and in all Macropodoidea. In all other marsupials, play was rudimentary or absent. Categorical rate of play was not correlated with body mass or with metabolic rate but was correlated with relative brain mass. The distribution of play in Australian marsupials supported the hypothesis that play acts to modify brain development.