Mitral annular calcification is a common echocardiographic finding. Caseous calcification is a rare variant seen as a large mass with echolucencies that resembles a tumor, occasionally resulting in exploratory cardiotomy. The aim of this study was to assess the prevalence of caseous calcification of the mitral annulus, to evaluate patient characteristics and the echocardiographic variables for diagnosing this entity, and to describe the clinical outcome on follow-up of such patients. Caseous calcification was defined as a large, round, echo-dense mass with smooth borders situated in the periannular region, with no acoustic shadowing artifacts and containing central areas of echolucencies resembling liquefaction. Eighteen patients were diagnosed by 2-dimensional echocardiography as having caseous calcification of the mitral annulus. One had calcification of the tricuspid annulus. Nine patients underwent transesophageal echocardiographic studies. A typical finding of a round, sometimes semilunar, large, echo-dense, soft mass with central echolucencies seen on both transthoracic and in particular transesophageal echocardiography, resembling a periannular mass, was demonstrated. The mass was posteriorly located in all mitral patients. Transesophageal echocardiography added limited information. Three patients underwent mitral valve replacement. The operative findings were a solid mass adherent to the posterior portion of the mitral valve. Sectioning revealed a toothpaste-like, white, caseous material. Sixteen (84%) patients were treated conservatively. On follow-up of 3.8 +/- 2.4 years, 4 patients died of unrelated causes. The characteristic appearance of a large, soft, echo-dense mass containing central areas of echolucencies resembling liquefaction at the posterior periannular region of the mitral valve on 2D echocardiography is compatible with the diagnosis of caseous abscess. Such a finding should not be confused with a tumor. Transesophageal echocardiography does not appear to contribute to the diagnosis. This rather impressive lesion appears to carry a benign prognosis.