Identity development can be challenging for adolescents, particularly those from immigrant families who are required to make sense of their identity whilst accommodating themselves into different cultures. For second-generation ethnic minority adolescents, these identity formation processes may range from harmony/effectiveness to conflict/stress, having consequences for acculturation and for mental health. Focusing on an underexplored area of research, the present study aimed to examine the relationships between ethnic identity, acculturation orientations, and mental health outcomes among second-generation Turkish adolescents (16-18 years old) in England. Data were collected using a self-report survey (N = 220) and analyzed using structural equation modelling. Results demonstrated that ethnic identity was positively associated with positive mental health and that each ethnic identity component (exploration, resolution, affirmation) was differently associated with life satisfaction, self-esteem, psychological well-being, and depression. Ethnic identity was also positively related to separation and negatively to marginalization whilst no relationships were observed between integration, separation or marginalization, and mental health. Mediation analysis determined that ethnic identity was negatively associated with assimilation and in turn, more positive mental health. Findings demonstrate the complexity of understanding the nature and effects of ethnic identity for second-generation adolescents and have important implications for theory and practice.