Background: The Cochrane Handbook for Systematic Reviews of Interventions (Version 4) defined a substantive update as a review that the authors and Review Group wished to highlight as a review that should be read again by people who had read it before, usually because of a change in conclusions. Authors should describe changes to the review since it was last published in the ‘What’s new’ section. Objectives: To assess what information is reported in the ‘What’s new’ section in Cochrane reviews marked as substantively updated in The Cochrane Library during 2007. Methods: Two people independently examined and extracted information from the ‘What’s new’ section of all substantively updated Cochrane reviews published in The Cochrane Library during 2007. Results: A total of 164 Cochrane reviews were substantively updated during 2007; 143 (87%) had some text in the ‘What’s new’ section. Of these, 29% (41/143) included the date the review had been updated, while 30% (43/143) gave the date of last search. Only 13% (18/143) specifically mentioned a change to conclusions, and a further 25% (36/143) stated that conclusions remained the same. Sixty-four per cent (91/143) of updated reviews used the ‘What’s new’ section to report the number of newly included studies, 34% (49/143) the number of newly excluded studies, and 8% (12/143) the number of new studies awaiting assessment. Very few updated Cochrane reviews mentioned changes to the review methods, outcomes, adverse events or new data from ongoing or previously unpublished trials in the ‘What’s new’ section. Conclusions: During 2007, the ‘What’s new’ section in Cochrane reviews, did not accurately reflect what had been updated. RevMan 5 gives more prominence to this section and should make it easier for authors to provide information that will make it easier for readers to identify changes in an updated review. RevMan 5 requires authors to mark the revised review in one of the following ways: ‘Amended’, ‘Feedback incorporated’, ‘New citation no major change’ or ‘New citation major change’. As before, they should also include a summary of the new information that has been added to the review.