RESUMEN
BACKGROUND: We consider whether nonsuicidal self-injury (NSSI) thoughts - in the absence of any NSSI behaviour - are associated with suicidal thoughts and behaviours among adolescents, before examining whether characteristics of NSSI behaviour are associated with greater suicidal thoughts and behaviours. METHODS: Adolescents (n = 2,057, M age =15.56) recruited from secondary schools reported their lifetime history of NSSI, suicidal thoughts and behaviours, NSSI characteristics, and NSSI functions. Receiver Operating Characteristic analysis test whether NSSI status and characteristics of NSSI behaviour are diagnostic of clinically elevated suicidal thoughts and behaviours (a score of 7 or higher on the Suicide Behaviours Questionnaire-Revised). Regression models test whether NSSI functions predict greater suicidality. RESULTS: Adolescents with NSSI thoughts and those with NSSI behaviour were more likely to report lifetime suicidal ideation and past-year suicide plan(s) than adolescents with no history of NSSI. In addition, adolescents with a history of NSSI were more likely to report a lifetime history of suicide attempt(s) as well as past-year suicide attempt(s) than adolescents with no history of NSSI. A greater number of NSSI methods, requiring medical assistance for NSSI injuries, and engaging in NSSI for self-punishment, anti-suicide, and sensation-seeking functions were associated with greater severity of suicidal thoughts and behaviours. LIMITATIONS: Data are cross-sectional, limiting inferences about causality. CONCLUSIONS: Findings emphasize the importance of NSSI thoughts and characteristics of NSSI behaviour in understanding the complex relationship between NSSI and suicidal thoughts and behaviours among adolescents.