The characteristics of the population of South Viet Nam are known only approximately, from sample surveys. The population, which is currently estimated to amount to 20 million people, is very young (59 % are aged under 20). This is due mainly to a large and unexplained shortfall in the age groups 20-40 years. The annual rate of growth is high (3 %) and urbanization is increasing fast; the urban population is overtaking that of the countryside. The death rate is estimated to be about 12 per thousand, corresponding to a life expectancy at birth (for both sexes) of about 55 years. Fertility is estimated to be in excess of 40 per thousand, equivalent to a completed family size of five live births per woman. A very high school attendance rate and a fair low low percentage of illiteracy suggest that fertility may drop in the future. There have recently been efforts to encourage the use of contraception.