Limited evidence exists about the effectiveness of parent/family-based interventions for preventing poor sexual health outcomes, thus a systematic review was conducted as part of a wider review of community-based sex and relationships and alcohol education. Method guidance from the UK's National Institute for Health and Clinical Excellence was adhered to. Overall, 18 databases were searched. In total, 12 108 references were identified, of which 440 were retrieved and screened. Overall, 17 studies met the inclusion criteria. Findings showed that parent-based interventions were inconsistently effective at reducing young people's sexual risk behaviours. Parent-based interventions had greater impact on parent/child communication than family-based interventions, which showed no evidence of effectiveness. However, increasing parent/child communication showed no effect on sexual risk behaviours. Preliminary evidence suggests that effectiveness was greater in those studies aiming to affect multiple risk behaviours. However, this may be due to longer programme delivery and follow-up times; further evidence is required. Sexual health communication was sensitive to intervention. Studies addressing multiple risk behaviours may be as effective as targeted interventions at affecting sexual risk behaviours. Longitudinal controlled studies, examining broader sexual activity outcomes, are needed in countries such as the United Kingdom to inform the evidence base, which is primarily US based, and contribute to related policies and practices.