The demand for medium term future population estimates for educational, labor force, and balanced overall planning in Thailand led to the examination and analysis of available census and vital registration data. The results of the 1960 census, taken after a lapse of 13 years, indicated that major changes in earlier population estimates may be necessary. This effort orginated in that context. The distinctiveness of the approach lies in its focus on local material. The demographic and administrative conditions in Thailand remained undisturbed during the last decade, and this provided a favorable setting for analysis of recent trends. Fertility was assumed to have remained nearly constant over the decades, while mortality improved slowly during earlier decades but at a much faster rate during the postwar period. Apart from the census, survey, and registration tabular material available, there have been few analytical studies on the population evolution of Thailand. Attention is directed to the following: primary estimates of vital rates from censuses and population projection. On the basis of the final adopted levels of registration, rates of their improvement, and the age sex differentials in registration, it was possible to make refined consistent estimates of the population at the early childhood range 0-4 at census 60. Expected population aged 0-4 from the finally adopted set of rates and differentials was 4.97 million, as against the 1st approximation of 5.15 million earlier from curve fitting (para 2.7), to give the finally adjusted population at census 60 as 26.99 million. This meant some consequential changes in the estimated birth and death rates, but they were very minor. Having estimated current levels and prevailing trends of the fertility and mortality components, assumptions as to their probable future course can be related to the past performance and of future developments in the field of family planning and public health in Thailand. According to projection, the pre adult 0-14 age proportion in the aggregate population declines from 45.0% in 1960 base to 40.6% in 1980. Under the assumed future course, the fall in fertility makes its effect felt on the projection first at the youngest age group 0-4 in 1970, and then progressively up to age group 101-4 in 1980. As compared to constant fertility, the declining fertility meant 4.78 million less population by 1980, about 10% difference in projected pre adult (0-14) population of the year.