Abstract: A total of 5271 references were screened and of these 23 RCTs met the inclusion criteria. Most were conducted in the USA and in health-care clinics (e.g. family planning). The majority of interventions provided information about STIs and taught safer sex skills (e.g. communication), occasionally supplemented with provision of resources (e.g. free sexual health services). They were heterogeneous in duration, contact time, provider, behavioural aims and outcomes. A variety of STIs were addressed including HIV and chlamydia. None of the trials explicitly mentioned HPV or cervical cancer prevention. Statistically significant effects for behavioural outcomes (e.g. increasing condom use) were common, though not universal and varied according to the type of outcome. There were no statistically significant effects of abstaining from or reducing sexual activity. There were few statistically significant effects on biological (STI) outcomes. Considerable uncertainty exists in the risk of bias due to incomplete or ambiguous reporting. Behavioural interventions for young women which aim to promote sexual behaviours protective of STI transmission can be effective, primarily at encouraging condom use. Future evaluations should include a greater focus on HPV and its link to cervical cancer, with long-term follow-up to assess impact on behaviour change, rates of HPV infection and progression to cervical cancer. Studies should use an RCT design where possible with integral process evaluation and cost-effectiveness analysis where appropriate. Given the predominance of USA studies in this systematic review evaluations conducted in other countries would be particularly useful.

Plain-language summary: Searches identified 5271 bibliographic records. Screening the records independently by two review authors identified 23 relevant randomised controlled trials (RCTs). The trials were mostly conducted in the USA (21 trials) and in health-care (e.g. family planning) clinics (14 trials), with only four in educational settings. Trial participants had mixed socio-economic and demographic characteristics and most were sexually experienced. The interventions mostly provided information about STIs and taught safer sex skills (e.g. communication with partners), occasionally supplemented with provision of resources (e.g. free sexual health services). Interventions varied considerably in duration, contact time, provider, behavioural aims and outcomes. A variety of STIs were addressed including HIV and chlamydia, but not explicitly HPV. The most common behavioural outcome (measured in 19 trials) was condom use for vaginal intercourse. Sexual partners, sexual abstinence and STIs were reported in four, two and 12 trials respectively. In terms of statistically significant effects, some interventions improved condom-related behaviour and reduced the number of sexual partners, but none affected the frequency of sexual episodes. Effects of interventions on STIs were limited. None of the interventions appeared to be harmful. The methods used in the trials were not always well described making it difficult to tell whether their results may have been biased. In conclusion, although some behavioural interventions improve condom-related behaviour, trials have been predominantly in USA healthcare settings, did not specifically address HPV and were too different to enable a most effective type of intervention to be identified.