Non-suicidal self-injury (NSSI) is common among adolescents in the general population, and it is the number one predictor of suicidal ideation and attempt. Neurodivergent adolescents have been underrepresented in the NSSI research literature, largely due to the overlap between repetitive self-harming behaviours that can be associated with neurodevelopmental conditions. Little is known about the extent to which neurodivergent adolescents engage in NSSI within Australia. Using data from the Longitudinal Study of Australian Children (LSAC; B and K cohorts), this study explored the rates of NSSI and suicidal behaviour in autistic (n=165), ADHD (n=239) and co-existing autism/ADHD (n=91) adolescents (aged 14 years) as compared to neurotypical peers (n=5795). Across all items, neurodivergent adolescents were significantly more likely to report NSSI and suicidal behaviour as compared to their neurotypical peers, including ‘thoughts of harming self’, ‘harming self on purpose’, ‘thoughts of attempting suicide’, ‘suicide plan’, and ‘suicide attempt’. What is more, young people with co-existing autism/ADHD were at greatest risk. Approximately 24% of autistic adolescents, 21% of adolescents with ADHD, and 24% of adolescents with co-existing autism/ADHD reported ‘thoughts of harming self’, compared to 16% of neurotypical peers. While 10%, 14% and 19% of autistic, ADHD and co-existing autism/ADHD adolescents, respectively, reported that they had hurt themselves on purpose (cf. 8% of neurotypical peers). Approximately 15%, 11%, and 20% of Autistic, ADHD, and co-existing autism/ADHD adolescents, respectively, had considered attempting suicide (cf. 9% of neurotypical peers). While 10%, 9% and 14% Autistic, ADHD, and co-existing autism/ADHD adolescents, respectively, had made a suicide plan (cf. 6% of neurotypical peers). The current findings highlight that there is a significant group of neurodivergent children who need targeted support to reduce and prevent NSSI and suicide.