The author examines the age structure of captive orang-utans in zoos and institutions. He shows that, unless breeding success can be achieved with captive-born animals – which so far no zoo in the world has done – zoo numbers will continue to decline, with little hope of replacement from the wild now that the International Convention on Trade in Endangered Species is in operation. John Perry is Assistant Director for Conservation at the National Zoo in Washington, and a Vice-Chairman of the IUCN's Survival Service Commission.