Background Record linkage is a useful tool for health research. Potential benefits aside, its use raises discussions on privacy issues, such as whether a written informed consent for access to health records and linkage should be obtained. The authors aim to systematically review studies that assess consent proportions to record linkage. Methods 8 databases were searched up to June 2011 to find articles which presented consent proportions to record linkage. The screening, eligibility and inclusion of articles were conducted by two (...) independent reviewers. The authors carried out meta-regression, subgroup and sensitivity analyses to assess heterogeneity. Results Of the 141 studies identified, only 11 presented empirical consent proportions and were included in the systematic review. The consent proportion varied widely from 39% to 97%. Seven studies presented consent proportions of 88% or higher, one of 72%, and only three presented consented proportion equal to or lower than 53%. None of the studies' characteristics evaluated explained heterogeneity. Conclusion The results of this review show that, in general, individuals tend to consent to the use of their data for record linkage, with exceptions in specific populations or minorities. The authors believe that this, as well as the cited literature, lends support to policies that, while keeping relevant ethical controls in place, do not require individual informed consent for each and every study that relies on secondary data. (shrink)