Introduction: Changes in fertility, mortality and migration components of the Sri Lankan population has changed significantly. It has grown almost eight times since the first national census of 1871, which recorded only 2.4 million people. The population size has increased from 14.8 million in 1981 to 18.7 million in 2001. The doubling of the population took place in 54 years between 1871 and 1925 and it doubled again in 35 years between 1925 and 1960. According to the standard projection, the population would reach 20.1 million by 2011, and could attain its peak by 2031 with a size of 21.1 million. A near-zero population growth rate would be attained during 2021 to 2036 where the total size of the population could be around 21 million. However beyond 2040, primarily, due to significantly low level of fertility, the total size of the Sri Lankan population would decline.