Background: Self-harm is a critical public health issue for adolescents/young adults. Aims: To estimate the prevalence of self-harm among adolescents with/without disabilities in the United Kingdom. Method: Secondary analysis of data collected at age 17 in the UK’s Millennium Cohort Study. Results: Prevalence of self-harm was significantly greater among adolescents with disabilities for suicide attempts and six forms of self-harming behaviors. The lifetime prevalence of suicide attempts was 5.3% (4.5–6.3) among adolescents without disabilities, 21.9% (18.2–26.2) among adolescents with less limiting disabilities, and 25.5% (17.2–35.9) among adolescents with more limiting disabilities. Adjusted prevalence rate ratios ranged from 5.13 (3.58–7.36) for those with mental health limitations to 1.48 (0.65–3.35) for those with mobility limitations. Similar patterns were observed for the 12-month prevalence of six self-harming behaviors. Limitations: Further studies are needed to identify potential mediators of the association between disability and self-harm that are potentially modifiable. Conclusion: Adolescents with disabilities are at markedly greater probability of suicide attempts and self-harming behaviors than their peers.