Since 1911 Thailand has taken frequent national censuses, and its National Statistical Office, working closely with a number of international agencies, was in the 1980s one of the most considerable sources of statistical information in Asia. One of the 20 most populous nations in the world, Thailand had in 1987 about 53 million people. This total was separated about equally between males and females. The regional breakdown was around 16.7 million in the Center (which included the Bangkok metropolitan area), 17.8 million in the Northeast, 11.3 million in the North, and 6.8 million in the South. As in most Southeast Asian nations, the population was youthful and agrarian; around 37 % of the population was between the ages of 15 and 29. In the decades after World War II, the %age of agricultural population declined; it decreased from 79.3 % to 72.3 % of the population between 1970 and 1980, for example.

Thailand's rush both to develop and to satisfy the demand for consumer products had several side effects, including dwindling agricultural land, the destruction of forests, and damage to watersheds. These consequences prompted the central government, with support from international agencies, to make a concerted effort to limit population growth. In 1968 the cabinet sanctioned a family-planning service, and by March 1970 a national population policy was announced. The official slogan "Many Children Make You Poor" and the economic arguments for keeping the number of children at two per family found acceptance among both city and rural populations. Successful programs were undertaken by the Planned Parenthood Association of Thailand and the Family Planning Services. By 1974 an around 25 % of all married couples of childbearing age were using modern contraceptives, one of the highest %ages for developing countries. The population growth rate, 3.4 % per annum in the 1960s, had been reduced to 1.9 % per annum by 1986. The goal for the late 1980s was a growth rate of 1.5 %.