Between 2002 and 2005, the NISDI perinatal cohort study recruited pregnant women from 15 sites across Argentina, the Bahamas, Brazil, and Mexico, who were at least 8 weeks of gestation and had tested positive for Human immunodeficiency virus (HIV). In 2006, two additional sites were added in Peru and Jamaica, and enrollment continued in all 17 sites until 2007. Over 1,100 pregnant women and over 1,100 babies were enrolled in the study. Participants were assessed at recruitment, three times before delivery, at delivery, at hospital discharge, at 6 - 12 weeks and 6 months postpartum. Children were followed up at birth, 6-12 weeks of age and 6 months of age. Women were eligible to enrol with subsequent pregnancies.