A best evidence topic was written according to a structured protocol. The question addressed was whether patients undergoing coronary bypass grafting and mitral intervention for moderate to severe ischaemic mitral regurgitation are best treated with mitral repair or replacement. Five hundred and fifty papers were found using the reported search. Based on the 14 non-randomised studies judged to represent best evidence, we concluded that whilst there is some evidence that the operative mortality may be less following mitral valve repair, long-term data are equivocal. Even with contemporary techniques, recurrent mitral regurgitation is not uncommon following repair. Replacement was more frequently performed for patients with greater co-morbidity. Whilst two studies attempted to control for this using propensity analysis, in the majority of studies this introduced considerable bias. No data was available on long-term functional outcomes and quality of life. As there is currently insufficient evidence to inform clinical practice, a randomised trial is warranted in this important area.