BACKGROUND: Several highly publicised rapes and murders of young women in India and South Africa have focused international attention on sexual violence. These cases are extremes of the wider phenomenon of sexual violence against women, but the true extent is poorly quantified. We did a systematic review to estimate prevalence. METHODS: We searched for articles published from Jan 1, 1998, to Dec 31, 2011, and manually search reference lists and contacted experts to identify population-based data on the prevalence of women's reported experiences of sexual violence from age 15 years onwards, by anyone except intimate partners. We used random effects meta-regression to calculate adjusted and unadjusted prevalence for regions, which we weighted by population size to calculate the worldwide estimate. FINDINGS: We identified 7231 studies from which we obtained 412 estimates covering 56 countries. In 2010 7.2% (95% CI 5.2-9.1) of women worldwide had ever experienced non-partner sexual violence. The highest estimates were in sub-Saharan Africa, central (21%, 95% CI 4.5-37.5) and sub-Saharan Africa, southern (17.4%, 11.4-23.3). The lowest prevalence was for Asia, south (3.3%, 0-8.3). Limited data were available from sub-Saharan Africa, central, North Africa/Middle East, Europe, eastern, and Asia Pacific, high income. INTERPRETATION: Sexual violence against women is common worldwide, with endemic levels seen in some areas, although large variations between settings need to be interpreted with caution because of differences in data availability and levels of disclosure. Nevertheless, our findings indicate a pressing health and human rights concern. FUNDING: South African Medical Research Council, Sigrid Rausing Trust, WHO.