This study of fertility trends in one of 10 countries involved in an Economic and Social Commission for Asia and the Pacific (ESCAP) project, measures fertility by small area, reflecting Thailand's from the bottom up planning policies. Section A describes the 4 regions physically and economically. National and regional fertility are also discussed, wide regional variations therein being a motivation for this study. The 1980 census showed mortality to be 39-58/1000 varying by region. Population policy has gone from pronatalist to one of population growth reduction, marital age increase and female education expansion. Section B stated an objective of acquiring information of low fertility reduction areas. A target figure of 1.5/1000 fertility is stated. Section C describes how fertility was indirectly measured using child-woman ratios from the 1980 census, adjusting for assumed underenmeration of children. Life expectancy was calculated as 65 for all of Thailand, ranging from 63-71 regionally. Underestimating child mortality might have caused overestimates of fertility. Section D outlines results: Changes in fertility from 1970-79 are -20.7%, -22.0%, -22.0%, -18.5%, -10.5%, and -20.4% for the Central, North, Northeast, and South regions, changes from 1964-76. A total fertility drop from 4.9% -3.9% was evidenced. Interregional differences and rural-urban differences in fertility change were dampered slightly. The fertility change phenomenon has spread out from defined foci, remaining high in outlying mountainous and forested regions, as shown by detailed maps. In section E, heavy concentration of program efforts in the outlying efforts is advised, continuing the successful multipoint supply efforts.