While many studies focus on the association between early life adversity and the later risk for psychopathology, few simultaneously explore diverse forms of environmental adversity. Moreover, those studies that examined the cumulative impact of early life adversity focus uniquely on postnatal influences. The objective of this study was to focus on the fetal period of development to construct and validate a cumulative prenatal adversity score in relation to a wide range of neurodevelopmental outcomes. We also examined the interaction of this adversity score with a biologically informed genetic score based on the serotonin transporter gene. Prenatal adversities were computed in two community birth cohorts using information on health during pregnancy, birth weight, gestational age, income, domestic violence/sexual abuse, marital strain, as well as maternal smoking, anxiety, and depression. A genetic score based on genes coexpressed with the serotonin transporter in the amygdala, hippocampus, and prefrontal cortex during prenatal life was constructed with an emphasis on functionally relevant single nucleotide polymorphisms, that is, expression quantitative trait loci. Prenatal adversities predicted a wide range of developmental and behavioral alterations in children as young as 2 years of age in both cohorts. There were interactions between the genetic score and adversities for several domains of the Child Behavior Checklist (CBCL), with pervasive developmental problems remaining significant adjustment for multiple comparisons. Scores combining different prenatal adverse exposures predict childhood behavior and interact with the genetic background to influence the risk for psychopathology.