Self-harm in adolescents is a global public health problem, with 10% of adolescents self-reporting selfharm within the past year1 and suicide the second commonest cause of death in young people aged 10–۲۴ years, after road traffic accidents.2 Self-harm in adolescents has serious consequences, and those who self-harm have a four times greater risk of death from any cause and a ten times greater risk of suicide than the general population,2–۴ indicating potentially avoidably high burdens of life-years lost and family and peer distress. Non-fatal repetition occurs in 18% of people who self-harm, according to a recent large multicentre study in England.5 A single effective intervention has not been identified.6 A recent systematic review and metaanalysis of 19 randomised controlled trials with 2176 participants found a small overall effect of three specific interventions (dialectical behaviour therapy, mentalisation-based therapy, and cognitive behavioural therapy) on repetition of self-harm.7 Studies with strong family involvement and substantial treatment dose showed significant reductions in self-harm events.7–۹ A recent large, retro-spective, registry-based matched cohort study (n=5678) showed lower long-term risk of self-harm in people receiving psychosocial treatments compared with those who did not, but numbers needed to treat were large.10 Family factors (parent–child interaction, perceived support, expressed emotion, experience of abuse, parental conflict, and parental mental health) are important risk factors associated with self-harm in children and adolescents.11 Family therapy aims to draw on and mobilise the existing strengths and resources of the child and family and is therefore a logical potential intervention after self-harm. This trial, termed the Self-Harm Intervention: Family Therapy (SHIFT) trial, reports on a new form of family therapy intervention for self-harm. The trial was done in response to a call by the National Institute for Health Research Health Technology Assessment programme for a study investigating the clinical effectiveness and costeffectiveness of family therapy for adolescents who selfharm (HTA 07/33). We aimed to assess the effectiveness of family therapy compared with treatment as usual in reducing self-harm repetition in young people.