BACKGROUND: Bereavement increases children's risk for psychological disorders, highlighting the need for effective interventions, especially in areas where orphanhood is common. We aimed to assess the effects of an eight-session support group intervention on the psychological health of bereaved female adolescents in South Africa. METHODS: This randomised controlled trial enrolled female adolescents at 11 schools in three peri-urban towns of Free State province, South Africa. 453 bereaved ninth-grade students aged 13-17 years who had expressed interest in taking part in the group were randomly assigned (1:1) to receive the intervention or to be waitlisted for programme enrolment after the study period and serve as the control group. The intervention, Abangane ("friends" in isiZulu), is a locally derived, curriculum-based support group focused on coping with loss incorporating indigenous stories and cognitive behavioural therapy components. Weekly group sessions were facilitated by trained social workers or social auxiliary workers from a local non-profit organisation. The primary outcomes included indicators of grief and depression as reported by adolescents and behavioural problems reported by their caregivers. Grief was measured with three scales: the grief subscale of the Core Bereavement Items to assess normative grief; and the Intrusive Grief Thoughts Scale and the Inventory of Complicated Grief-Revised for Children to assess maladaptive grief symptoms in the past 4 weeks. Depression symptoms in the past 7 days were measured with the Center for Epidemiological Studies-Depression Scale for Children. Caregivers completed the Brief Problem Monitor-Parent Form to report on adolescent's behaviour in the previous 4 weeks. Analysis was intention to treat. This study is registered with ClinicalTrials.gov, number NCT02368808. FINDINGS: Between Sept 30, 2014, and Feb 5, 2015, eligible female participants were identified, of whom 226 were assigned to the intervention, Abangane, and 227 were assigned to the waitlisted control group. Analysis included 382 adolescents who completed both surveys (193 participants assigned to Abangane and 189 assigned to waitlist). At follow up, the intervention group had significantly lower scores for primary outcomes, including intrusive grief (p=0·000, Cohen's d=-0·21), complicated grief (p=0·015, d=-0·14), and depression (p=0·009, d=-0·21) relative to the waitlisted group, while core bereavement scores were similar between groups (p=0·269). Caregivers in the intervention group reported lower levels of behavioural problems among adolescents (p=0·017, d=-0·31). INTERPRETATION: Short-term, structured, theory-based support groups with contextually relevant content show promise in mitigating psychological and behavioural problems among bereaved adolescents. Abangane is replicable in resource limited settings, using freely available curriculum materials, existing programme structures, and appropriately trained personnel to implement it. FUNDING: US Agency for International Development Southern Africa.