This chapter examines factors such as neglect, social overstimulation and psycho-social deprivation that might exacerbate or provoke autistic-type behaviours. It draws on studies of Romanian children who spent their infancy in state institutions in conditions that offered little physical contact with caregivers and very low levels of stimulation, leading to social difficulties and repetitive behaviours as the infants matured. Many of the children were later adopted into UK and Romanian families; broadly, the longer the children spent in institutional care, the more profound and prolonged their difficulties. Autism can also affect a child’s relationship with their environment; overstimulating social environments can result in the repetitive movements known among autistics as ‘stimming’. Such behaviours, viewed by the clinical community as pathological, can in fact be adaptive strategies that help autistics meet the demands of challenging environments. A tentative conclusion is that the earlier in the life course a risk is encountered, the more trait-like and less state-like the resulting autistic behaviours appear to be.