The SCDS began in the mid-1980s and aims to study child development in the Republic of Seychelles, as well as to study factors, such as diet, that may modulate associations between mercury exposure and child development. The study consists of four cohorts: the pilot cohort, comprised of 789 children who joined the study in 1986 and who have been intermittently followed for child development ever since; the main cohort, recruited in 1989 and comprised of 779 children, which has been tested for developmental outcomes at 6, 19, and 29 months and again at 5.5, 9, 10.5, 17, 19, 22, and 24 years of age; the nutrition cohort 1, consisting of 300 infants enrolled in 2001; and the nutrition cohort 2, consisting of 1,535 infants recruited between 2008 and 2011.