To certify the continuity between the normal and prolapsed mitral valves (MVP), two-dimensional and color Doppler echocardiography (2-DE and CDE) were performed for healthy 250 male subjects of 13 years old. The distance from the plane of the mitral annulus to the coaptation (c) and the grade of systolic ballooning of the anterior mitral leaflet as expressed by the maximum distance between the leaflet and the straight line connecting the anterior mitral ring with the point of coaptation (d) were measured in the long-axis 2-DE. Mitral regurgitation (MR) was evaluated by CDE. Distribution of c was between +10 and -3 mm, and d was between +5 and -3 mm (minus denotes prolapse toward the left atrium). An approximately normal distribution was found in both parameters c and d. The incidence of MVP varied from 3 to 13% according to the strictness of the criteria for MVP. Subjects with MR from the posterior commissure showed the coaptation significantly displaced toward the atrium compared with the rest of subjects (p less than 0.01). Our data suggest that MVP is a multifactorial disorder of the valve and the development of MR has some relation to the severity of MVP.