Internal security problems from the 1960s up until 1998 prevented any fieldwork in Cambodia. Since then, the situation has improved greatly and the Royal Government of Cambodia, in collaboration with international conservation NGOs, has been conducting general biological surveys across the country. Survey reports were used to investigate current occurrence of hornbills. Historically, three hornbill species — Great Hornbill Buceros bicornis, Wreathed Hornbill Aceros undulatus and Oriental Pied Hornbill Anthracoceros albirostris — were known from Cambodia. Recent surveys show that populations of Great and Wreathed Hornbills have declined significantly since the 1960s, while Oriental Pied is still common. A fourth hornbill species, Brown Hornbill Anorrhinus tickelli, was reported in 1998 in Kirirom National Park spanning the border of Koh Kong and Kompong Speu provinces in south-west Cambodia. Conservation priorities and priorities for future surveys are being developed.