BACKGROUND: People with Borderline Personality Disorder (BPD) have limited access to long term psychological therapies. Briefer interventions have been developed but trial evidence to support their use has not been reviewed. AIMS: To examine whether psychological interventions for adults with BPD of six months duration or less improve symptoms, mood, self-harm, suicidal behaviour, and service use. METHODS: The protocol was prospectively registered (PROSPERO CRD42017063777). Database searches were conducted up to April 2020. Inclusion, data extraction and risk of bias were assessed in duplicate. We identified 27 randomised controlled trials. We conducted random-effects meta-analyses sub-grouping data into delivery method, additional support, and comparison type. RESULTS: High levels of bias were found for attrition and reporting. Heterogeneity was high in some pooled data. Borderline symptom reductions were greatest for interventions including additional support (SMD. -1.23, 95% C.I. -2.13, -0.33). Planned generic support may be as effective as specialist interventions for borderline symptoms (SMD = -0.11, 95% C.I. -0.51, 0.29) and social functioning (SMD = -0.16., 95% C.I. -0.65, 0.33). Follow-up was limited and direct comparison with post-intervention results was unreliable. CONCLUSIONS: Short-term interventions may be effective. Access to additional support has an impact on outcomes. It is unclear if symptomatic change is sustained.