Bukit Lawang's famous orang-utan centre was set up in 1973 to help primates readjust to the wild after captivity or displacement through land clearing. Much of the original duties of the centre have been moved to more-remote locations, but twice-daily feedings are still provided to semi-dependent orang-utans. These events are open to the public (no guide required) and provide one of the closest views of the forest ape outside the confines of a zoo.

During the centre's decades-long career, it has introduced 200 orang-utans into the jungle and many of them have successfully mated with the wild population. Before releasing the animals into the jungle, the centre teaches the orang-utans, many of whom have been kept as caged pets, how to forage for food in the wild, build nests, climb trees, and other essentials for survival. The orang-utans are also treated for diseases that they contracted during contact with humans.

Once the apes are on their own in the wild, the centre still provides feedings to supplement awkward transitions or demanding circumstances. The feedings provided by the centre consist of milk and bananas and are considered a fairly bland diet compared with the diversity of food found in the forest. The semi-wild apes who appear at the centre's 'welfare' platform are typically nursing or pregnant females in need of an extra source of nutrition.

There are two feeding times a day: 08:30 to 09:30 and 15:00 to 16:00. These are the only times visitors are allowed to enter the national park without a guide.

The feeding platform is located on the west bank of Sungai Bohorok within the park boundaries, about a 20-minute walk from the village. The river crossing to the park office is made by dugout canoe. Perlindungan Hutan dan Konservasi Alam (PHKA; Directorate General of Forest Protection and Nature Conservation) permits are required to enter the park (20,000Rp, plus 500Rp insurance) and are available from the office at the foot of the trail to the platform.

Since 1996 the centre has been closed to new arrivals, as the park is considered saturated with orang-utans. A replacement quarantine centre, just outside Medan, opened in 2002 to carry on the rehabilitation efforts, but it is not open to the public. Originally funded by World Wildlife Fund and Frankfurt Zoological Society, the centre now falls under the management of the Indonesian government, which does not provide adequate budgetary resources. Park rangers are not paid in a timely fashion and permit money is sent directly to Jakarta. Despite these problems, the rangers are dedicated to their jobs and often supplement their incomes and their hands-on experience by working with foreign researchers.

Outside Gunung Leuser National Park, orang-utans can be found in the Tanjung Puting and Kutai National Parks, in the Gunung Palung and Bukit Raja Reserves in Kalimantan, as well as in neighbouring Sarawak and Sabah in Malaysia.

For more information about Sumatran orang-utans try the Sumatran Orangutan Society (www.orangutans-sos.org) and the Sumatran Orangutan Conservation Programme (www.sumatranorangutan.com).