To estimate the sex-specific effect of herpes simplex virus type 2 (HSV-2) on the acquisition of HIV infection. The increased number of longitudinal studies available since the last meta-analysis was published allows for the calculation of age- and sexual behaviour-adjusted relative risks (RR) separately for men and women. Systematic review and meta-analysis of longitudinal studies. PubMed, Embase and relevant conference abstracts were systematically searched to identify longitudinal studies in which the relative timing of HSV-2 infection and HIV infection could be established. Where necessary, authors were contacted for separate estimates in men and women, adjusted for age and a measure of sexual behaviour. Summary adjusted RR were calculated using random-effects meta-analyses where appropriate. Studies on recent HSV-2 incidence as a risk factor for HIV acquisition were also collated. Of 19 eligible studies identified, 18 adjusted for age and at least one measure of sexual behaviour after author contact. Among these, HSV-2 seropositivity was a statistically significant risk factor for HIV acquisition in general population studies of men [summary adjusted RR, 2.7; 95% confidence interval (CI), 1.9-3.9] and women (RR, 3.1; 95% CI, 1.7-5.6), and among men who have sex with men (RR, 1.7; 95% CI, 1.2-2.4). The effect in high-risk women showed significant heterogeneity, with no overall evidence of an association. Prevalent HSV-2 infection is associated with a three-fold increased risk of HIV acquisition among both men and women in the general population, suggesting that, in areas of high HSV-2 prevalence, a high proportion of HIV is attributable to HSV-2.