Estimates of the number of people who perished under the Khmer Rouge vary tremendously. A figure of three million deaths between 1975 and 1979 was given by the Vietnamese-sponsored Phnom Penh regime, the PRK. Father Ponchaud suggested 2.3 million. Amnesty International estimated 1.4 million dead the United States Department of State, 1.2 million. Khieu Samphan and Pol Pot, who could be expected to give underestimations, cited figures of 1 million and 800,000, respectively. In 1962 the year of the last census taken before Cambodia was engulfed by war, the population of the country was cited at 5.7 million. Ten years later, in 1972, the population was estimated to have reached 7.1 million. Using Pol Pot's rather modest figure of 800,000 deaths, about 11 percent of the population would have died from unnatural causes between 1975 and 1978. By contrast, Amnesty International's figure would yield a death rate of almost 20 percent of the population Father Ponchaud's, of approximately 32 percent. The revolution was easily, in proportion to the size of the country's population, the bloodiest in modern Asian history.

As is evident from the accounts of refugees, the greatest causes of death were hunger, disease, and exposure. Many city people could not survive the rigors of life in the countryside, the forced marches, and the hard physical labor. People died from the bites of venomous snakes, drowned in flooded areas during the rainy season, and were killed by wild beasts in jungle areas. Many fell victim to malaria. Others died in the fighting between Vietnam and Cambodia in 1978 and in 1979. Nonetheless, executions accounted for hundreds of thousands of victims and perhaps for as many as 1 million. Western journalists have been shown "killing fields" containing as many as 16,000 bodies.

Data as of December 1987