Two rehabilitation centres have been operative in Gunung Leuser National Park, 8,080 sq km (830,000 ha) of mainly hill dipterocarp forest. Gunung Leuser is one of the largest and most important national parks in Asia (Payne & Andau, 1989). When these rehabilitation centres were opened, and until the 1980s, Gunung Leuser had only reserve status (Aveling, 1982). In mid-1980, a complex of reserves was combined to become Gunung Leuser National Park, one of Indonesia’s first national parks. About half the range is mountainous (> 1800 m) and sub-optimal orangutan habitat.