The 2004 Pelotas Birth Cohort is one of four large population-based cohorts based within the Brazilian city of Pelotas. The first cohort is from 1982, and the development of a new cohort begins every 11 years (1982, 1993, 2004, and 2015). Members within the current cohort consist of all live babies born from 1 January to 31 December 2004 to women living in the urban area of the city of Pelotas, Brazil. After a first assessment at the time of birth, all cohort participants were assessed at ages 3, 12, 24, and 48 months and at age 6 years, with follow-up rates of 95.7%, 94.3%, 93.5%, 92.0% and 90.2%, respectively. More recently, participants were assessed at ages 11, 15 and 17 years.