Echocardiography has been accepted as the diagnostic modality of choice for mitral valve prolapse (MVP). The determine the effect of position on echocardiographic diagnosis of MVP, we examined 693 consecutive patients referred to the echocardiography laboratory because of suspected MVP. First, patients were examined using the usual standard M-Mode echocardiography( left parasternal third or fourth intercostal space, supine or left decubitus) and two dimensional echocardiography ( apical 4 chamber view, parasternal long axis view). Echocardiography on erect position was performed in patients with normal standard echocardiogram (M-MODE and two- dimensional). On the basis of echocardiographic results, three groups of patients were compared: group 1: 201 patients with MVP on standard echocardiogram had mid systolic click= MSC(53.7℅) and late systolic murmur = LSM(29.4℅) in auscultation. Group 2: 247 patients with MVP on erect position had MSC(15.4℅) and LSM(4.9℅),( p<0.001, compared with group 1). Group 3:245 cases without MVP on any position had MSC (4.1℅) and LSM (0.8℅), compared with group 1&2). The results of the study show that: 1: standard echocardiography is the best method for diagnosis of MVP. 2: echocardiography on erect position is a valuable method in patients with MSC or LSM in auscultation without MVP on standard echocardiography.3: combined echocardiography and auscultation improves accuracy of MVP diagnosis.