The ecology of the Patagonia puma was studied in Torres del Paine National Park, Chile. Thirteen pumas were captured from 1986 to 1989 and equipped with radio transmitters. During the winter of 1988 there was one puma per 17 km2 in the 200 km2 study area. Home ranges varied from 24 to 107 km2. Female home ranges overlapped with those of other males and females extensively, but male ranges overlapped each other for only short time periods. Seven adult pumas had home ranges extending outside the park boundaries and at least three preyed on sheep. Guanacos Lama guanicoe, especially young animals, were the puma's most important prey item by biomass, but European hares Lepus capensis were preyed upon more than expected relative to available biomass. Of 731 guanaco skulls collected from 1979 to 1988, 33% showed clear evidence of having been killed by pumas. Over the past decade puma numbers are believed to have increased in the park, perhaps in response to an increase in guanaco numbers and continued protection. With decreased hunting pressure and harassment by horses and dogs, pumas have habituated to people and are being observed more often by park visitors.