A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether mitral valve repair at the time of coronary artery bypass grafting (CABG) in patients with coronary artery disease and mild to moderate mitral insufficiency improves short and long-term outcome. Altogether 465 papers were found using the reported search, of which 16 presented the best evidence to answer the clinical question. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results, and study weaknesses of these papers are tabulated. We conclude that there is good evidence to suggest that moderate mitral regurgitation in patients undergoing isolated CABG adversely affects survival and mitral regurgitation does not reliably improve after CABG alone. Unfortunately, the evidence to support mitral valve repair at the time of CABG to improve long-term survival is still weak. On balance, patients with moderate ischaemic mitral regurgitation having CABG should have mitral repair at the same time, although the evidence to support this is weaker than one might like.