Background: International comparisons of the costs of interventions are important for a number of different applications. One specific application relates to systematic reviews that aim to incorporate evidence on the costs of interventions collected from included studies. Since included studies are often conducted in different countries and/or at different times, estimates of costs are often expressed in different currencies and/or price years. In these circumstances adjustment of costs to a common target currency and price year is necessary to facilitate meaningful comparisons and synthesis of the evidence across studies. Methods: A web-based tool utilising GDP deflator indices and Purchasing Power Parities conversion rates was programmed using C#. The tool automates adjustment of costs to target currency and price year. Results: Version 1.0 is available for use by authors of systematic reviews and other analysts, free of charge, at http://eppi.ioe.ac.uk/costconversion/default.aspx. Conclusions: This tool can be used as a first-line approach to cost adjustment in systematic reviews of social and behavioural interventions and as a optional approach in systematic reviews of health care interventions where more sophisticated methods of adjustment are not feasible. Its benefits include increased speed and accuracy of adjustments and use of an explicit, reproducible methodology consistent with the systematic review process.