BACKGROUND: Self-harm by young people is occurring with increasing frequency. Conventional in-patient and out-patient treatment has yet to be proved efficacious. AIMS: To investigate the efficacy of a short cognitive-behavioural therapy intervention with 90 adolescents and adults who had recently engaged in self-harm. METHOD: Participants (aged 15-35 years) were randomly assigned to treatment as usual plus the intervention, or treatment as usual only. Assessments were completed at baseline and at 3 months, 6 months and 9 months follow-up. RESULTS: Patients who received cognitive-behavioural therapy in addition to treatment as usual were found to have significantly greater reductions in self-harm, suicidal cognitions and symptoms of depression and anxiety, and significantly greater improvements in self-esteem and problem-solving ability, compared with the control group. CONCLUSIONS: These findings extend the evidence that a time-limited cognitive-behavioural intervention is effective for patients with recurrent and chronic self-harm.