The objective of this paper was to document mercury contamination of Amerindian populations living along the Beni River in Bolivia and to examine risk factors related to their lifestyle. A cross-sectional survey was performed among 15 communities on the flood plains of the Beni River at the foothills of the Andes. Hair mercury content (H-Hg) served as a bioindicator of mercury contamination. Mercury values were available for 556 people. Four indicators of lifestyle were analyzed: community accessibility, subsistence activity, fish consumption, and ethnicity (i.e., members of the Tacana or Ese Ejja ethnic group). The median of H-Hg was equal to 4.0 microg/g (95% CI [confidence interval] = 3.6-4.4). Approximately 86% of the subjects had H-Hg values lower than 10 microg/g. No significant differences existed in H-Hg between adult women and children, nor according to age group. Subjects belonging to the Ese Ejja ethnic group had higher H-Hg than subjects from the Tacanas ethnic group. Communities accessible only by canoe were more frequently contaminated than those accessible by road. Subjects who ate at least one serving of fish per day had higher H-Hg, and families who maintained substantial fishing activity were more strongly contaminated. Contamination levels were found to be low compared with other Amazonian studies. The most strongly affected groups, however, were those which preserved a traditional way of life and were the most economically and socially disadvantaged.