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For many herbivorous mammal species across the world, geophagy, the consumption of soil, is an important method for obtaining minerals, especially sodium. However, this behavior has not been recorded in marsupials. The eastern grey kangaroo (Macropus giganteus), an intensively studied macropod species, is known to use physiological and micromorphological adaptations to conserve sodium. We present results of another adaptation, the use of natural licks, by this species and 3 other macropod species at Sundown National Park, Australia. Natural licks had significantly higher levels of sodium, magnesium, and sulfur than surrounding soils. We examined patterns of lick use by kangaroos to test 3 possible proximate causes of geophagy: whether lick use was affected by dietary mineral content, life-history stage, and thermoregulation. The number of kangaroos visiting the licks increased with temperature and mean cloud cover, varied among months, and was marginally significantly influenced by dietary mineral content. Visit durations to one lick increased with temperature and were influenced by month and life-history stage; females with high lactation demand and large males spent the most time at the lick. The proportion of time spent in geophagy when at a focal lick varied with month and reproductive state. Therefore geophagy is not restricted to eutherian mammals, and kangaroos, like many eutherian species, appear to adjust this behavior in response to their mineral demand. Geophagy in kangaroos is facultative, rather than obligative, and has not been detected in other intensively studied populations. In areas of Australia with low levels of sodium, high temperatures, and suitable lick sites, geophagy may play a key role in marsupial ecology.