Objective: Little is known about self-stigma experienced by young people with mental health problems, despite the fact that research has demonstrated its existence. In the present study, we sought to investigate the experiences of self-stigma in childhood and adolescence, and particularly the nature of change in self-stigma across this developmental period. Young adults diagnosed with attention-deficit/hyperactivity disorder (ADHD) or depression before their 18th birthdays were interviewed about their experiences within their peer groups during childhood and adolescence. Methods: This qualitative study involved open-ended interviews with 16 young adults aged 18-30 years. Interviews focused on the experience of stigmatization, responses to stigma, and how these changed over time. Results: Three main themes pertaining to self-stigma emerged: (a) being different, (b) peer stigmatization and associated experiences of self-stigma, and (c) selective disclosure and a move toward greater openness. The findings also suggested that the passing of time and changes in young people's social networks and/or degrees of recovery were associated with changes in their experiences of self-stigma. Conclusions and Implications for Practice: During childhood and adolescence, self-stigma is characterized by a sense of being different from peers and negative self-evaluation as a consequence of that difference. However, our findings also demonstrated that some young people were prepared to challenge the stigma they experienced. Further research is needed to understand the factors that contribute to these differing responses and to develop antistigma interventions that facilitate the inclusion of young people with mental health problems in their peer groups.