BACKGROUND AND OBJECTIVES: We sought to characterize the lesion characteristics of mitral valve prolapse (MVP), which is being increasingly recognized as a cause of mitral regurgitation (MR) in Koreans SUBJECTS AND METHODS: 497 Patients with MVP that was diagnosed by echocardiography in 13 university-affiliated hospitals from Jan to Dec 2003 were prospectively enrolled in our study. RESULTS: A total of 497 patients (270 males, 54%) were enrolled and their mean age was 52+/-17 years. Grade 4 MR was present in 272 patients (54.7%); grade 3, 2 and 1 MR as present in 30.2%, 10.7% and 4.2%, respectively. MVP of the anterior and posterior mitral leaflet was present in 170 patients (34.2%) and 223 patients (44.9%), respectively; MVP developed in both leaflets in 104 patients (20.9%). In 37 patients (7.4%), MVP developed in all 6 segments of the mitral leaflet and these patients were younger (37+/-14 versus 54+/-16 years, respectively, p<0.05) and had a lower prevalence of chordae rupture and severe MR compared to the other patients. Among the 266 mitral segments showing prolapse in the 132 patients (26.6%) who underwent transesophageal echocardiography, the posterior medial scallop was the most frequently diseased one (26%), and this was followed by the posterior middle scallop (18%), the medial (17%), lateral (14%) and middle (13%) part of the anterior leaflet, and the posterior lateral scallop (12%). Younger patients with a mean age <45 years showed a lower prevalence of single segment prolapse, hypertension, severe MR and chordae rupture compared to the older patients (p<0.001, each). CONCLUSION: The medial part of both mitral leaflets was the predilection site for the development of MVP in Koreans and the lesion characteristics were different according to the patients' age.