The role of genetics in criminal behaviour can be assessed through family, twin and adoption studies. This paper discusses the major findings of adoption studies that have focused on criminal outcome. Results from adoption studies have consistently revealed a relationship between biological parent criminal behaviour and adoptee criminal outcome. This finding has been noted in the case of property crime, but not in the case of violent crime. Violent crime in adopted-away offspring is not related to violent crime in biological parents. Findings from the Danish Adoption Cohort suggest that violent crime may be genetically related to other types of behavioural deviance. In the Danish Adoption Cohort, there is an increased rate of schizophrenia in the adopted-away offspring of biological fathers who are convicted of violent crimes. This father violence-adoptee schizophrenia relationship cannot be accounted for by the potential confounding factors of rearing social status, age at transfer, knowledge of family history of crime, or biological parents' mental illness.