Introduction: Deliberate self-poisoning is one of the most common methods of self-harm among adolescents worldwide and represents a significant public health concern in Sri Lanka. However, comprehensive evidence on psychosocial and contextual risk factors remains limited. Objectives: To identify independent psychosocial, familial and school-related risk factors associated with deliberate selfpoisoning among Sri Lankan adolescents. Methods: A multicentre prospective case–control study was conducted over two years in selected tertiary care hospitals in Sri Lanka. Adolescents aged 10–17 years admitted with deliberate poisoning were recruited as cases, with age- and sex-matched controls selected from the same hospitals. Structured interviews assessed sociodemographic characteristics, psychiatric history , family environment and school-related factors. Conditional logistic regression was used to estimate adjusted odds ratios (AORs). Results: A total of 326 case–control pairs (n=652) were included; 74.5% of cases were female and most were aged 15– 17 years. Paracetamol (45.1%) and oleander (10.7%) were the most frequently ingested agents. In multivariable analysis, independent risk factors included personal history of psychiatric illness (AOR 2.76), previous self-injury (AOR 4.17), previous deliberate poisoning (AOR 4.02), non-heterosexual orientation (AOR 26.9), school dropout (AOR 4.01), exposure to home violence (AOR 8.93) and persistent feelings of depression (AOR 2.08). Female sex and older adolescent age were also overrepresented among cases. Conclusions: Adolescent deliberate poisoning in Sri Lanka is strongly associated with psychiatric vulnerability , family adversity , identity-related distress and school disengagement. Strengthening adolescent-friendly mental health services, early schoolbased screening and targeted psychosocial interventions is urgently needed.