The Asiatic wild ass Equus hemionus, or khulan, once ranged across much of Central Asia, but is now globally threatened. The largest free-ranging populations are now restricted to a 250-km wide area (range 100–400 km) across the Gobi Desert region of southern Mongolia. Over the last 23 years the population has moved further north and east into its former range. Surveys conducted in the 1970s and 1980s estimated that the Mongolian population contained fewer than 15 000 animals and was declining as a result of human exploitation and livestock competition. Aerial surveys (one in autumn 1994, two in spring 1997) were flown as line transects over portions of the khulan's range in Mongolia and ground surveys (five in spring, summer, and autumn 1994–97) were conducted by vehicle and foot. Sample sizes and areas surveyed were larger than previous surveys, and our methods were often more systematic. Population size was estimated at 33 000–63 000 wild asses in Mongolia. Animal density ranged from 4.2±1.3 to 19.1±3.2 per 100 km2. Mean group size ranged from four to 35 animals in the south-western Gobi, four to seven animals in the southern Gobi, and three to 18 in the south-eastern Gobi. Our data suggest that Mongolia is the most important stronghold for the conservation of E. hemionus. Conservation management continues to be challenging because intensive studies on khulan biology and ecology are just beginning. As a free-market economy continues to emerge in Mongolia, pressure from resource extraction interests and nomadic livestock herders to remove the khulan's protected status, permit harvesting and halt population growth and expansion, also makes implementation of research and conservation management programs more imperative.