Using 69 new life tables recently made by Arriaga for Latin American countries by stable-population methods, the authors examine the mortality trends for more countries and more periods of history than have previously been available for analysis. For the late nineteenth and early twentieth centuries, the new tables yield a substantially lower life-expectancy than that shown by previously published life tables; for recent decades the difference is smaller, though in the same direction. As a consequence, the new tables show a speed of mortality decline in Latin America greater than the speed hitherto assumed. When the trend is analyzed in terms of economic development, it appears that the decline was extremely slow in the more backward Latin American countries until around 1930, whereas in the more advanced countries of the region, a more rapid decline had set in before that. After 1930, however, in both groups of countries the pace of decline was faster than ever, and it was virtually the same for both groups, suggesting that after that date public health measures were exerting a strong influence independently of local economic development. This result is confirmed by comparison with the past history of now developed countries; the mortality decline in Latin America after 1930 was much faster than it was historically at the same level in the industrial countries. As compared with other underdeveloped countries today, the unprecedented decline of mortality in Latin America is typical. In most underdeveloped countries, whether in Latin America or elsewhere, mortality change seems increasingly independent of economic improvement and more dependent on the importation of preventive medicine and public health from the industrial countries.