Environmental mercury contamination in French Guiana stems from gold mining activities carried out in the late 19th and 20th centuries. Studies were conducted between 1994 and 2005 to measure mercury exposure levels in the Guyanese population and track changes over time among the most exposed populations. These were cross-sectional surveys conducted on a sample of randomly selected individuals. Mercury exposure in most communities in French Guiana remains moderate. However, the surveys revealed excessive mercury exposure among Amerindian populations and confirmed that this exposure is indeed linked to a diet rich in fish, some species of which are heavily contaminated, and also identified the species contributing most to exposure. While the levels of mercury accumulation measured to date are below the concentrations at which clinically observable neurological abnormalities and congenital malformations have been observed in Japan, the tests conducted have shown that at these exposure levels, there are moderate signs of impaired neurological or neurobehavioral development in children. Thus, fetuses and newborns are the two population groups that must be prioritized for protection. (R.A.)