This study tests the hypothesis that mitral annular calcium (MAC) detected by transthoracic echocardiography (TTE) is a marker for high prevalence and severity of coronary artery disease (CAD) in patients undergoing coronary angiography. Pathological studies have suggested that there is an association between MAC and calcific deposits in coronary arteries; however, there are no clinical data to support this association. One hundred sixty-five patients with MAC (101 women and 64 men; mean age 71 ± 8 years) who underwent cardiac catheterization with coronary angiography for various reasons were compared with 147 age-matched controls without MAC who underwent coronary angiography for the same indications during the same period. MAC was defined as a dense, localized, highly reflective area at the base of the posterior mitral leaflet detected by TTE. Obstructive CAD was defined as either ≥50% reduction of the internal diameter of the left main coronary artery or ≥70% reduction of the internal diameter of the left anterior descending, right coronary, or left circumflex artery distribution. Compared with controls, the MAC group had a significantly higher prevalence of CAD (89%vs 75%, p = 0.001) and higher rates of 3-vessel disease (45% vs 24%, p = 0.001) and left main CAD (13% vs 5%, p = 0.009). Nonsignificant CAD was more common in the control group (25% vs 11%, p = 0.001). Multivariate analysis identified MAC (p = 0.0002), indications for cardiac angiography (p = 0.02), sex (p = 0.03), and diabetes mellitus (p = 0.03) as independent predictors for the presence and severity of obstructive CAD. MAC detected by TTE may be a marker for high prevalence and severity of CAD in patients undergoing coronary angiography.