<p>Deliberate self-harm in adolescents is a significant public health problem, associated with a range of psychiatric comorbidities, and with serious consequences for the individual and their family. This study aimed to examine the impact of demographic (gender and age), interpersonal (family functioning) and intrapersonal (borderline personality disorder, suicidal ideation and impulsivity) factors on deliberate self-harm. Method: A cross-sectional study was employed to collect data from 744 secondary school-based adolescents. The data were collected using valid self-report measures, specifically the Family Adaptability and Cohesion Evaluation Scale IV, the Borderline Personality Features Scale for Children, the Suicidal Ideation Questionnaire, the Inventory of Deliberate Self-Harm Behaviours and the Barrat Impulsivity Scale. Hierarchical multiple linear regression was employed for data analysis. Results: The results showed that gender, age and family functioning, were significant in dependent predictors of deliberate self-harm. However, when intrapersonal factors such as borderline personality disorder and suicidal ideation were included in the equation model, the effect was reduced. Among these factors, suicidal ideation emerged as the most significant predictor, followed by borderline personality disorder, whereas impulsivity was not an effective direct predictor. Conclusions: Findings suggest that intrapersonal factors, particularly suicidal ideation and borderline personality disorder, have a stronger effect on deliberate self-harm than demographic and interpersonal factors. This highlights the fundamental need for prevention and intervention strategies that integrate mental health treatment and family support. These findings have significant implications for clinical practice and provide a robust foundation for future research on effective interventions for at-risk adolescents.</p>