Self-harm is a critical public health issue for adolescents/young adults. To estimate the prevalence of self-harm among adolescents with/without disabilities in the United Kingdom. Secondary analysis of data collected at age 17 in the UK's Millennium Cohort Study. 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. Further studies are needed to identify potential mediators of the association between disability and self-harm that are potentially modifiable. Adolescents with disabilities are at markedly greater probability of suicide attempts and self-harming behaviors than their peers.