OBJECTIVES: To determine the additional prognostic value of mitral regurgitation (MR) over B-type natriuretic peptide (BNP), left ventricular ejection fraction (LVEF) and clinical characteristics in patients with acute coronary syndromes (ACS). DESIGN: Long-term follow-up in a prospective ACS cohort with Doppler-assessed MR, echocardiographically-determined LVEF and plasma BNP levels by ELISA. SETTING: Single-centre university hospital. PATIENTS: 725 patients with ACS. MAIN OUTCOME MEASURES: Death and readmission for congestive heart failure. RESULTS: During a median follow-up of 98 months, 235 patients (32%) died. Significant MR (grade >1 of 4) was found in 90 patients (12%). In a multivariate model including MR grade >1, LVEF <0.40 and BNP >373 pg/ml (75th percentile), MR was significantly associated with long-term mortality (HR 2.28, 95% CI 1.67 to 3.12; p<0.0001). When also adjusting for conventional risk factors, MR remained significantly associated with mortality (HR 1.53, 95% CI 1.06 to 2.19; p=0.02), as well as with congestive heart failure (HR 2.08, 95% CI 1.29 to 3.35; p=0.003). CONCLUSIONS: MR is common in patients with ACS, provides independent risk information and should be taken into account in the evaluation of the long-term prognosis.