Although anthropometric information on South American Indian populations has been collected for many years, remarkably little is known about age-related changes in their body size in adulthood. The lack of baseline information on the normal pattern of aging among Amerindian adults hinders investigations into the health consequences of the many economic, environmental and demographic changes that are currently occurring among South American Indian populations. This study presents data on the body size and shape of a convenience sample of 345 Patamona and 186 Wapishana Amerindian adults over 20 years of age living in the remote interior of Guyana. Analysis of the cross-sectional data demonstrated significant declines in stature, sitting height, and biacromial width with age, while there were no changes in subischial leg length or arm length across the age range of the study populations. In contrast, body weight and body mass index (BMI--a measure of body fatness) only declined in those over 50 years of age, after a period of increase. Significant differences in adult linear body dimensions were found between the two Amerindian populations that were proposed to be the result of known differences in childhood growth performance. However, the greater BMI of the Wapishana was shown to be associated with their significantly greater current wealth, thereby highlighting the presence of biological consequences of wealth inequalities even within these subsistence farming populations.