The relation between fertility and cultural change in a Peruvian Amazon Indian village was studied initially in 1964 and in more detail in 1969. The 1969 study included observations concerning social, economic, environmental, cultural, and health changes. Population growth in the village is nearly 5% per year, and fertility appears to exceed that previously recorded for other groups. The factors that may be contributing to the high fertility are explored. They are thought to include early and prolonged parity, nearly universal marriage and fertility, high reproductive efficiency, short birth intervals, Western health intervention lowering both infant and maternal mortality rates, and a decline in the prevalence of polygyny.