Eligible cumulative meta-analyses had sometimes been done as part of the planning process for a new study to explore how the evidence base had evolved. Studies were not included if only surrogate outcome measures were used unless – like blood pressure and severe anaemia, for example – these were unambiguously important. The searches also identified cumulative metaanalysis in other types of health research but these were not eligible for this review. We wished to identify published reports containing graphs of cumulative meta-analyses. An initial search of Pubmed Clinical Queries using the term ‘cumulative meta-analysis’ retrieved 822 records. The selected papers were screened by one author,JJKK-048 who selected a set of 23 records which were added to a set of core articles that had been previously identified as part of this author’s general interest in this area. This full set of papers were then analysed to obtain ideas for free-text search terms and index or MeSH terms for use in a final search strategy. Nearly all of the cumulative meta-analyses had been conducted as retrospective exercises to explore how the evidence base had evolved. However, some were used to inform the design of a new study. For example,KYA1797K potassium salt Algra and van Gijn presented a cumulative meta-analyses which was used to inform the need for the European and Australian Stroke Prevention in Reversible Ischaemia Trial. A variety of themes were apparent from the cumulative metaanalyses and these are illustrated here with specific examples. A detailed explanation is not provided for each cumulative metaanalyses, but the citations for all the included studies are available in Appendix S1. The included studies showed that initially positive results became null or negative in the meta-analysis as more trials were done; that early null or negative results were over-turned; that stable results would have been seen had a meta-analysis of existing evidence been done before the new trial; and that additional trials had been much too small to resolve the remaining uncertainties.