International Childhood Cancer Cohort Consortium (I4C). The International Childhood Cancer Cohort Consortium is a project in which birth cohorts throughout the world are pooled to study prospectively risk factors for childhood cancers. Leukemia, including acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML), is the most common type of childhood cancers in most Western populations. For this reason, the I4C will initially concentrate on conducting studies of etiology of childhood leukaemia. The I4C will focus on questions that this collaboration can best answer and that require longitudinal data collection in very large populations. Initial studies will use available prospective data to assess exposures postulated to cause specific types of childhood leukemia as suggested by past work based primarily on case-control studies. Four studies are currently underway that are evaluating risk of pediatric leukemia including assessment of birth weight, folic acid from diet and supplements, parental occupation, and surrogate measures of pesticides based on nearby crops (ascertained using geocoding). A pilot study will assess whether differences in DNA methylation can be detectable in offspring at birth, assessing microRNA expression and global DNA methylation in cord blood and Guthrie cards in relation to birth weight.