Preterm birth and exposure to childhood sexual abuse (CSA) are early physiological and psychological adversities that have been linked to reduced social functioning across the lifespan. However, the joint effects of being born preterm and being exposed to CSA on adult social outcomes remains unclear. We sought to determine the impact of exposure to both preterm birth and CSA on adult social functioning in a group of 179 extremely low birth weight (ELBW;2500 g) participants in the fourth decade of life. Social outcome data from a prospective, longitudinal, population-based Canadian birth cohort initiated between the years of 1977 and 1982 were examined. At age 29-36 years, ELBW survivors who experienced CSA reported poorer relationships with their partner, worse family functioning, greater loneliness, lower self-esteem and had higher rates of avoidant personality problems than those who had not experienced CSA. Birth weight status was also found to moderate associations between CSA and self-esteem (P=0.032), loneliness (P=0.021) and family functioning (P=0.060), such that the adverse effects of CSA were amplified in ELBW survivors. Exposure to CSA appears to augment the adult social risks associated with perinatal adversity. Individuals born preterm and exposed to CSA appear to be a group at particularly high risk for adverse social outcomes in adulthood.