The purpose of this study was to assess the nutritional status of the adult Suruı´ population, an indigenous society from the Brazilian Amazon, as it relates to socioeconomic conditions. Fieldwork was carried out in February– March 2005, including 252 individuals (88.1% of the total eligible subjects older than 20 years of age in the villages surveyed). Anthropometric measurements were performed following standard procedures, and percentage of body fat (%BF) was measured by bioimpedance. To classify the Suruı´ according to socioeconomic status (SES), an index was constructed based on a group of variables to characterize socioeconomic differentiation. Evaluated by body mass index (BMI), the majority of Suruı´ 20–49.9 years of age were overweight (42.3%) or obese (18.2%). The frequency of obesity for women (24.5%) was twice that recorded for men. Subjects classified as overweight or obese also showed high %BF and waist circumference (WC). Women in the high SES category showed higher anthropometric values (including weight, BMI, arm fat area, and WC) and %BF than those of lower SES. This study shows that the Suruı´ are undergoing a rapid process of nutrition transition. This transition is closely associated with the emergence of intragroup differences in SES which have impacted diet and physical activity patterns. In research in indigenous peoples in Amazonia, greater attention should be paid to the human biological outcomes of socioeconomic transformations related to the growing involvement of native societies in the market economy. Am. J. Hum. Biol.