Studies suggest that children who have experienced neglect are at risk for bullying which in turn increases the risk for poor mental health. Here we extend this research by examining whether this risk extends to the neglect associated with severe institutional deprivation and then testing the extent to which these effects are mediated by prior deprivation-related neuro-developmental problems such as symptoms of inattention, hyperactivity and autism. Data were collected at ages 6, 11, 15, and young adulthood (22-25 years) from 165 adoptees who experienced up to 43 months of deprivation in Romanian Orphanages in 1980s and 52 non-deprived UK adoptees (N = 217; 50.23% females). Deprivation was associated with elevated levels of bullying and neuro-developmental symptoms at ages 6 through 15 and young adult depression and anxiety. Paths from deprivation to poor adult mental health were mediated via cross-lagged effects from earlier neuro-developmental problems to later bullying. Findings evidence how deep-seated neuro-developmental impacts of institutional deprivation can cascade across development to impact social functioning and mental health. These results elucidate cascade timing and the association between early deprivation and later bullying victimization across childhood and adolescence.