Objective To evaluate the effectiveness of current medical and psychological interventions for individuals at risk of sexually abusing children, both in known abusers and those at risk of abusing.Design Systematic review of interventions designed to prevent reoffending among known abusers and prevention for individuals at risk of sexually abusing children. Randomised controlled trials and prospective observational studies were eligible. Primary outcomes were arrests, convictions, breaches of conditions, and self reported sexual abuse of children after one year or more.Results After review of 1447 abstracts, we retrieved 167 full text studies, and finally included eight studies with low to moderate risk of bias. We found weak evidence for interventions aimed at reducing reoffending in identified sexual abusers of children. For adults, evidence from five trials was insufficient regarding both benefits and risks with psychological treatment and pharmacotherapy. For adolescents, limited evidence from one trial suggested that multisystemic therapy prevented reoffence (relative risk 0.18, 95% confidence interval 0.04 to 0.73); lack of adequate research prevented conclusions about effects of other treatments. Evidence was also inadequate regarding effectiveness of treatment for children with sexual behavioural problems in the one trial identified. Finally, we found no eligible research on preventive methods for adults and adolescents who had not sexually abused children but were at higher risk of doing so (such as those with paedophilic sexual preference).Conclusion There are major weaknesses in the scientific evidence, particularly regarding adult men, the main category of sexual abusers of children. Better coordinated and funded high quality studies including several countries are urgently needed. Until conclusive evidence is available, realistic clinical strategies might involve reduction of specific risk factors for sex crimes, such as sexual preoccupation, in abusers at risk of reoffending.