History and Objectives: Mitral valve prolapse is the most common of the valvular diseases, especially its posterior cusp as cited in references. In this respect, there is little information for its incidence in Iranian children. This study was carried out to determine its incidence in 50 neonates referred to echocardiography ward to Shaheed Beheshti hospital in Kashan.

Materials and Methods: The descriptive strategy of this study was performed on 50 neonates and children with mitral prolapse and with auscultation it was as non-ejection click or without end-systolic murmur. The echocardiography was performed in M-mode, two-dimensional and color Doppler and data were analyzed statistically.

Results: Out of 50 studied children and neonates, 29 cases (58%) were female and 21 cases (40%) were male and their age was from 2 months to 13 years. In 48 cases (96%) only the anterior cusp was involved. In one case (2%) there was prolapse of posterior cusp and in 1 other case (2%), both cusps were involved. In 4 patients (8%) there existed mild mitral failure and in 46 of them (92%), there was no valvular failure. Out of 4 patients with mitral failure, 3 cases were male and one of them was female.

Conclusion: In contrast to existing information in available references, the most common involvement of patients with mitral prolapse is anterior cusp failure. This difference can be attributed to regional, racial and genetic factors.