The ability to regulate emotions is crucial for well-being and adaptive social functioning. Emotional disorders commonly emerge in adolescence, a period characterized by changes in emotion and emotion-related processes, making emotion regulation a principal developmental task. Concurrently, the brain undergoes large structural and functional changes. We investigated relationships between two emotion regulation strategies, cognitive reappraisal and expressive suppression, and development of cortical thickness, as well as amygdala and nucleus accumbens volumes. A total of 112 participants (59 females) aged 8-19 at inclusion were followed for up to 3 times over a 7-year-period, providing 272 observations. Participants completed the Emotion Regulation Questionnaire (ERQ), yielding measures of cognitive reappraisal and expressive suppression. Relations between emotion regulation and brain development were analyzed using linear mixed models. Contrary to expectations, volumetric growth of amygdala and nucleus accumbens was not associated with either emotion regulation strategy. However, frequent use of expressive suppression was linked to greater regionally specific apparent cortical thinning in both sexes, while cognitive reappraisal was associated with greater regionally specific apparent thinning in females and less thinning in males. In contrast to the traditionally emphasized role of frontal control regions in cognitive reappraisal, the results also imply involvement of cortical regions associated with social cognition and semantics.