Anthropometric and household data (size, composition, economic activity) were collected from a population of Ribeirinhos living in a rural setting in the eastern Amazon. Data are compared to international reference standards and to other Amazonian populations with the goals of increasing our understanding of the Amazon's largest ethnic group and identifying the relationship between changes in subsistence strategies and nutritional status. Data on height, weight, skinfolds, and circumferences were collected from 471 adults and subadults. The population showed a high degree of stunting with an average HAZ below −2.0 for all age groups over 3 years, and 60% of adult men and 70% of adult women were stunted. Wasting was rare. Average skinfold thicknesses and upper-arm muscle area were near or below average but within the normal range compared to the reference standard, indicating adequate energy and protein stores. Thirty-one percent of males and 29% of females were overweight/obese, and the highest average BMIs were found among men and women in their 40s. Adult males who participated in wage labor had higher weights, BMIs, and UMA values, and were more likely to be overweight and obese compared with those who did not work in wage-labor jobs. Children of fathers who worked in wage labor had higher BMI and UMA values, but there was no significant effect on the nutritional status of other adults in these same households. Signs of the nutrition transition were most noticeable among adult males involved in wage labor because of changes in their diet and activity patterns. Am J Phys Anthropol, 2007. © 2007 Wiley-Liss, Inc.