Fertility estimates for Thailand in the period 1953-79 are derived by a newly extended procedure for reconstructing birth histories from «own-children birth histories», applied to the censuses of 1970 and 1980. From the reconstructed birth histories, period parity progression ratios from women's own birth (parity 0) to first marriage, from first marriage to first birth (parity 1), and from each parity to the next are calculated for the period 1953-79. Age-specific fertility rates for 1955-79 are computed as well. The data and results indicate significantly greater underreporting of children ever born in the 1980 census than in the 1970 census. Nevertheless, there is clearly a true decline with time in progression from parity 0 to first marriage, from first marriage to parity 1, and from each parity to the next, although the rate of decline from first marriage to parity 1, and from parity to parity 2, is slight. The decline in each case begins in the 1960s. For progression to parity 3 or higher, the rate of decline is very steep. Perhaps most surprising is the rate of decline in progression from parity 0 to parity 1, which is greater than that from parity 1 to parity 2