The aim of this study was to investigate whether adolescents born extremely preterm differ from full-term born regarding mental health, social support and attachment style. Fifty-one young adults born before the 29th gestational week and 54 born at term were investigated by self-reports. Psychological health was measured by the Beck Youth Inventories of Emotional and Social Impairment, social support with the Interview Schedule of Social Interaction and attachment style with the Relationship Questionnaire. No difference was noted regarding mental health. The preterm group described themselves as having less social interaction (p ≤ 0.001), but no difference was obtained regarding satisfaction with this circumstance. The prematurely born judged a preoccupied attachment style, concordant with a model of a negative self and positive other, to be applicable more often than the controls (p = 0.02). Extremely preterm born adolescents did not experience more problems regarding mental health compared to controls. Nevertheless, they reported less social interaction and, to a greater extent, a negative model of self.