Background The COMET Initiative is developing a publically-accessible online resource to collate the knowledge base for core outcome set (COS) development and implementation. This will be used by trial funders, trialists and researchers to see what has been done in their area of interest, and by research funders wishing to fund new work in this area who want to avoid unnecessary duplication of effort. This requires the development and application of an optimal, multi-faceted search strategy to identify work related to the development of COS.