A 61-year-old woman had acromegaly associated with mitral regurgitation (MR) resulting from prolapse of the posterior mitral leaflet. At the age of 51 years, the patient was diagnosed with hypertension and a cardiac murmur. She had the characteristic acromegalic appearance, but without visual disturbance. Blood chemistry revealed an elevated plasma concentration of growth hormone and glucose intolerance. Echocardiography showed remarkable dilation of the left ventricle and prolapse of the anterolateral commissure with severe MR. Magnetic resonance imaging of the brain revealed a pituitary microadenoma. MR was successfully corrected by quadrangular resection of the posterior leaflet, including the prolapsed portion, and prosthetic ring annuloplasty. The patient recovered uneventfully. (Circ J 2002; 66: 522 -524)