--- - |2+ Background Individuals born extremely preterm are exposed to significant perinatal stresses that are associated with an increased risk of psychopathology. However, a paucity of longitudinal studies has prevented the empirical examination of long‐term, dynamic effects of perinatal adversity on mental health. Here, internalizing and externalizing problems from adolescence through adulthood were compared in individuals born at extremely low birth weight (ELBW; <1,000 g) and normal birth weight (NBW; >2,500 g). Methods Internalizing and externalizing data were collected over 20 years in three waves, during adolescence, young adulthood, and adulthood. Growth models were used to compare longitudinal trajectories in a geographically based sample of 151 ELBW survivors and 137 NBW control participants born between 1977 and 1982 matched for age, sex, and socioeconomic status at age 8. Results After adjusting for sex, socioeconomic and immigrant status, and family functioning, ELBW survivors failed to show the normative, age‐related decline in internalizing problems over time relative to their NBW peers (β = .21; p < .01). Both groups exhibited small declines in externalizing problems over the same period. Self‐esteem (but not physical health, IQ, or maternal mood) partially mediated the association between ELBW status and internalizing problems. Conclusions Extremely low birth weight survivors experienced a blunting of the expected improvement in depression and anxiety from adolescence to adulthood. These findings suggest that altered physiological regulatory systems supporting emotional and cognitive processing may contribute to the maintenance of internalizing problems in this population. - Journal of Child Psychology and Psychiatry, Volume 59, Issue 11, Page 1192-1200, November 2018.