Background: The Cochrane Collaboration has a policy that Cochrane reviews should be updated every two years. However, there is limited evidence to suggest that this, or any other time period, is the ideal interval between updates. Updating too early may introduce bias, and too late may lead the end user to act on out of date or potentially misleading information. A change to current procedures for updating Cochrane reviews is needed to replace the current ad hoc and arbitrary approach with one that is more evidence-based. Objectives: To develop and validate a tool to help assess the need and likely benefits of updating a Cochrane review. Methods: An international Steering Committee was established. The updating tool was developed from empirical evidence on updating systematic reviews, guidance in the new Cochrane Handbook for Systematic Reviews of Interventions (version 5), RevMan 5, work by the Cochrane Updating Working Group, and checklists from various agencies, including Cochrane Review Groups. The tool will be enhanced and refined through formal piloting and input from users and experts involved in updating Cochrane reviews. Results: Step 1 of the tool is a decision tree which identifies triggers for updating a Cochrane review. These include new evidence, new methods, response to feedback or other factors, such as the age of the review or its use in policy and guidelines. If a review author decides that a trigger, for example the availability of a new study, is likely to change the conclusions of their review, a checklist (Step 2) helps them consider which sections of the review require updating. The checklist is an itemised guide through the review process which may or may not lead to updating of specific sections of the review. Conclusions: We hope that this tool will make it easier to identify which Cochrane reviews are ripe for updating and ensure that the decision-making process is made clearer and more transparent to the end user. (Funded by the Cochrane Opportunities Fund.)