The age as an important factor influencing the prognosis of mitral valve prolapse (MVP) was assessed by comparing two age groups; 26 cases whose ages were younger than 49 years, and 27 cases more than 50 years. 1. The aged group had higher incidence of dyspnea and enlarged heart most probably due to insidious heart failure. 2. The aged group frequently had an apical pansystolic murmur and enlarged left atrium, indicating the progress of mitral regurgitation. These observations suggest that the careful follow-up observation is mandatory for patients with MVP of advanced age.