The clinical characteristics of 107 patients younger than 60 years with mitral anular calcium (MAC) were compared with those of 107 age- and sex-matched control subjects. The patients with MAC included 55 men and 52 women, mean age 51 years. The control group included 55 men and 52 women, mean age 51 years. Patients with MAC had a higher prevalence of cardiomegaly on chest x-ray (p less than 0.0001), left atrial and left ventricular enlargement by echocardiography (p less than 0.0001), precordial murmurs (p less than 0.0001), diabetes mellitus (p less than 0.0001), systemic hypertension (p less than 0.025) and total conduction defects on surface electrocardiograms (p less than 0.0001) compared with the age- and sex-matched control subjects. The mean serum phosphorus and product of serum calcium and phosphorus were higher in patients with MAC (p less than 0.0025) than in the control subjects. The prevalence of coronary heart disease, aortic stenosis and hypertrophic cardiomyopathy and the mean serum cholesterol, triglyceride, total protein, albumin, creatinine, alkaline phosphatase and calcium levels were not significantly different between patients with MAC and the control subjects.