Arenophryne rotunda is a small (2–8 g) terrestrialfrog that inhabits the coastal sand dunes of centralWestern Australia. While sand burrowing is a strategyemployed by many frog species inhabiting Australia’ssemi-arid and arid zones, A. rotunda is unique amongburrowing species because it lives independently of freewater and can be found nocturnally active on the dunesurface for relatively extended periods. Consequently,we examined the physiological factors that enable thisunique frog to maintain water balance. A. rotunda wasnot found to have any special adaptation to reduce EWL(being equivalent to a free water surface) or rehydratefrom water (having the lowest rehydration rate measuredfor 15 Western Australian frog species), but it wasable to maintain water balance in sand of very lowmoisture (1–2%). Frogs excavated in the field were indune sand of 4.4% moisture content, as a consequenceof recent rain, which was more than adequate for thesefrogs to maintain water balance as reflected by their lowplasma and urine osmotic concentrations. We suggestthat in dry periods of the year, A. rotunda can achievepositive water balance by cutaneous water uptake byburrowing deeper into the substrate to where the percentwater content is greater than 1.5%.