Mitral annulus calcification (MAC), while a relatively frequent autopsy finding in older patients, is rare in childhood. Such calcification has generally been regarded as a degenerative change and of no clinical significance. Recent studies have shown that MAC may be associated with hemodynamically significant lesions including mitral insufficiency, arrhythmias, heart block, and, rarely, mitral stenosis. We have studied a case of massive calcification in the mitral annulus in a 17-year-old girl with juvenile rheumatoid arthritis and systemic lupus erythematosis. In this case, the MAC was considered secondary to the rheumatoid disease. MAC in younger patients with no history of rheumatic fever or bacterial endocarditis suggests an associated connective tissue disorder.