BACKGROUND: Increased global access and use of HIV antiretroviral therapy (ART) has been postulated to undermine HIV prevention efforts by changing individual risk-taking behaviour. This review aims to determine whether ART use is associated with changes in sexual or injecting risk-taking behaviour or diagnosis of sexually transmitted infections (STIs). METHODS: A systematic review and meta-analysis was conducted of HIV-seropositive participants receiving ART compared to no ART use in experimental or observational studies. Primary outcomes included: (1) any unprotected sexual intercourse; (2) STI diagnoses; and (3) any unsafe injecting behaviour. RESULTS: Fifty-eight studies met the selection criteria. Fifty-six studies containing 32,857 participants reported unprotected sex; eleven studies containing 16,138 participants reported STI diagnoses; and four studies containing 1,600 participants reported unsafe injecting behaviour. All included studies were observational. Unprotected sex was lower in those receiving ART than those not receiving ART (odds ratio (OR) 0.73, 95%CI 0.64-0.83, p<0.001; heterogeneity I2=79%) in both high-income (n=38) and low-/middle-income country (n=18) settings, without any evidence of publication bias. STI diagnoses were also lower among individuals on ART (OR 0.58, 95%CI 0.33-1.01, p=0.053; I2=92%), however there was no difference in injecting risk-taking behaviour with antiretroviral use (OR 0.90, 95%CI 0.60-1.35, p=0.6; I2=0%). CONCLUSIONS: Despite concerns that use of ART might increase sexual or injecting risk-taking, available research suggests unprotected sex is reduced among HIV-infected individuals on treatment. The reasons for this are not yet clear, though self-selection and mutually reinforcing effects of HIV treatment and prevention messages among people on ART are likely.