BACKGROUND Despite current interest in attachment disorder, there is concern about its discrimination from other disorders and an unproven assumption of an environmental aetiology. OBJECTIVE To test whether behaviours suggestive of attachment disorder are distinct from other childhood behavioural and emotional problems and are solely environmentally determined. METHODS In a community sample of 13,472 twins, we carried out factor analysis of questionnaire items encompassing behaviours indicative of attachment disorder, conduct problems, hyperactivity and emotional difficulties. We used behavioural genetic model-fitting analysis to explore the contribution of genes and environment. RESULTS Factor analysis showed clear discrimination between behaviours suggestive of attachment disorder, conduct problems, hyperactivity and emotional problems. Behavioural genetics analysis suggested a strong genetic influence to attachment disorder behaviour, with males showing higher heritability. CONCLUSIONS Behaviours suggestive of attachment disorder can be differentiated from common childhood emotional and behavioural problems and appear to be strongly genetically influenced, particularly in boys.