Throughout the Khmer Rouge period (1975–79) and especially after Vietnam's invasion toppled the regime in early 1979, hundreds of thousands of Cambodians fled westward toward the Thai border to escape violence, famine, and continued fighting between Vietnamese forces and remaining Khmer Rouge and other resistance factions. Large camps such as Khao-I-Dang and Sa Kaeo housed as many as 600,000 refugees at the peak of the crisis in the early 1980s, supported by a major international relief effort after initial chaos and forced Thai pushbacks in 1979 drew global attention. Many refugees spent a decade or more in camp limbo before the 1991 Paris Peace Accords ended the conflict, after which the UN Transitional Authority in Cambodia (UNTAC) repatriated roughly 370,000 people in 1992–93.
Cambodians fled Khmer Rouge rule and the subsequent Vietnamese occupation into refugee camps along the Thai border, later repatriated under UN supervision
There was no census between 1962 (5.7 million) and 1998, so April 1975 figures are reconstructions; they range from about 7.1 to 7.9 million. The 1998 census counted 11.4 million and shows the sex-ratio and cohort deficits left by 1975-79.
No comprehensive toll exists for the exodus itself. The largest single documented loss was Thailand's forced pushback of tens of thousands of Cambodians down a mined escarpment at Preah Vihear in June 1979, where relief workers, diplomats and later researchers estimated deaths from mines, falls and exhaustion in the hundreds to around 3,000; further deaths accumulated from shelling of the border camps, landmines and banditry through the 1980s. Mass mortality inside Cambodia under the Khmer Rouge and in the 1979 famine is counted separately.
Asia Watch (later Human Rights Watch) and the Lawyers Committee for Human Rights documented confinement of refugees in closed camps under Thai Task Force 80, rape and extortion by security forces and bandits, and forced labour and military conscription in the Khmer Rouge-administered border camps.
Cambodia, Thailand